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Spotting the Thread
aka: Spot The Thread

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"A web of lies can unravel with the lightest touch of the truth!"
Othar Tryggvassen (Gentleman Adventurer!), Girl Genius

This is when an impersonator has an almost perfect disguise, only to ruin it with a seemingly inconspicuous mistake. Perhaps the impostor blurted out something out-of-character (or a personal catchphrase), forgot to include a Distinguishing Mark (often an Intimate Mark), or accidentally revealed that they're left-handed. This can more easily occur during a round of Bluff the Imposter, and can be a sub-trope of Spot the Impostor except that their target generally has no advance knowledge that there is an impostor in the first place.

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Related to Pull the Thread as this is often what leads to it. Compare Saying Too Much, a more incriminating version. See also Conviction by Counterfactual Clue, when this gets even more unrealistic, and Conviction by Contradiction, which overlooks that there may be a perfectly reasonable explanation for the discrepancy. Often overlaps with Imposter Forgot One Detail. Compare For Want of a Nail.

When applied to a dream test, it's A Glitch in the Matrix or a Revealing Continuity Lapse. See also I Never Told You My Name and I Never Said It Was Poison, when the impostor gives themselves away by revealing they know something they shouldn't.


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Examples:

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    Advertising 
  • Played for Laughs in a Bush's Baked Beans Ad:
    Talking dog dressed as ghost: How did you know it was me?
    Human: Grandpa didn't have a tail.

    Anime & Manga 
  • Done in Alive: The Final Evolution, where one of Big Bad Katsumata's Comrades was a female Body Surfer named Han sent to infiltrate the American military by entering the body of one of James McPherson's subordinates to locate the Mineral MacGuffin "the heart of Akuro". Despite possessing the memories of his host body, Han is eventually shot in the heart by McPherson when he notices that his subordinate keeps his nails unusually clean and manicured.
  • In Ascendance of a Bookworm Lutz realizes that given Maine's background she shouldn't know how to create paper, hair ornaments or shampoo and calls her out on it. She doesn't deny it, but he eventually decides it doesn't really matter who she is since the original Myne isn't coming back and he never knew that girl anyway.
  • Attack on Titan:
    • Armin can even identify the scratches and dings on Marco Bott's 3D Maneuver Gear when he sees Annie Leonhart present it for inspection in place of their own gear, to prevent anyone from realizing that she'd used her own gear to kill "Sawney" and "Bean", the captured Titans being used as test subjects.
    • Reiner and Bertolt had a Conveniently Unverifiable Cover Story and avoided associating with their co-conspirator, to avoid any suspicion. But one mistake leads to them being suspected — their falsified documents listed them all as coming from the same region.
      • The other bit of damning info came when Armin remembered that during the 57th expedition, Reiner had been overtly interested in figuring out where Eren was; and, after a run-in with the Female Titan, she had changed course.
    • While examining a crate full of canned goods, Ymir complains about it being Herring, a food they don't particularly like. Their companion is shocked, because the label is in another language and therefore shouldn't be possible to read.
    • Much later in the manga Eren sneaks into Marley disguised as a wounded soldier, but puts his Eldian armband on the wrong arm. Subverted in that he's never found out; the one person to notice is Naïve Newcomer Falco, who assumes that Eren's suffering from Shell-Shock and puts it on the right arm for him. Too late, Falco spots a second thread; if "Kruger" met Reiner more than four years ago, it was probably while Reiner was infiltrating the Island of Paradis, meaning that the "friend" is an Eldian and an enemy.
  • Axis Powers Hetalia:
    • England runs afoul this trope in the Can't Escape from Italy strips. His Italian disguise is eventually perfected with the help of a spy, right down to taping a curl to the side of his head, but Germany sniffs him out when England stands posturing instead of hitting on the attractive women who pass by.
    • Germany himself is outed by France when he starts mashing his potatoes up instead of slicing them.
  • Claymore: Raki is told that a Claymore is looking for him and is in the nearby forest. When they talk Raki points out, correctly, that Claymores never refer to themselves as Claymoresnote . The Reveal is that it was a Yoma impersonating a Claymore to take him hostage in order to draw Clare out and kill her.
  • Twice in Fullmetal Alchemist:
    • The first time is where Maes Hughes catches out the shape-shifter Envy because he forgot a mole when he took the appearance of Maria Ross.
    • The second time is where Riza catches Envy out again when he took the appearance of Roy Mustang, claiming that they were on a First-Name Basis when alone, but then admitting that she lied when he panicked - played with in this case, in that she fakes this trope in order to expose him.
  • In Hunter × Hunter, the group see a human couple being attacked by a Shapeshifter. However, this turns out to be a Secret Test of Character that's part of the Hunter Exams. Kurapika notices a "thread" that was put there on purpose: the woman has (fake) tattoos that indicate a Vow of Celibacy, despite her supposedly being married. Gon, meanwhile, notices that the "monster" whom he's pursuing actually switches out with a different member of their species partway through the chase—this surprises and amuses them, since humans can never tell them apart.
  • In chapter 42 of Inside Mari, Isao delivers the Wham Line "Let's lie down here together again sometime" when describing what Mari had told Yori in the nurse's room. The problem is Yori never mentioned that Mari said that to her. It's one of the most concrete signs that this isn't really a bodyswap manga.
  • The Lupin III franchise has Lupin calling Zenigata "Tot-san" ("Pops" or "Old Man" in English dubs). In the Lupin IIIVS Detective Conan Made-for-TV Movie, Zenigata identifies the disguised Lupin when Lupin calls him by his nickname.
  • Mahou Sensei Negima!:
    • The Takamichi illusion during the Bad Future Rescue Arc.
    • Also done humorously, when Negi realizes that the Shizuna-sensei he's speaking to is an impostor because of a Marshmallow Hell. Turns out that the impostor (Asakura) didn't quite measure up to Shizuna's bust size.
  • In Monster, Tenma is initially suspicious with two "friendly" helpers being accomplices of Johan and has his suspicions confirmed when one of them refers to him as "doctor" — something he never told them about.
  • In one Mysterious Joker chapter, a kid detective tries to help a pair of siblings open a special safe to claim their deceased father's inheritance. Near the end, the detective reveals that the siblings are actually thieves who tied up the real family and assumed their identities in order to trick him into opening the safe so they could steal its contents. He claims to have realized this upon noticing that despite supposedly being trained musicians, none of the siblings had calluses on their hands.
  • Naruto:
    • Sasuke recognizes a Naruto impostor because he doesn't have a cut on his cheek (Naruto received it before they entered the Forest of Death.), and also because the impostor is left-handed while Naruto is right-handed. After this incident, the team decides to have a secret password, so if they split up and someone comes back, they can confirm their identity via the password. Naruto promptly is separated from the group, rejoins them, and recites the password correctly. Sasuke promptly attacks. The real point of the password was to see if a Naruto impostor could recite it correctly- the real Naruto would never remember the intentionally long and complicated password, especially on his first try.
    • Early in the series, Kohonamaru is spotted trying to trail Naruto, as he is holding his fence-colored camouflage in the wrong direction.
    • Much later on, Sakura recognizes that Neji is being impersonated by a White Zetsu, because the impostor fails to realize that Tonton is a pig.
  • In the Alabasta arc in One Piece, the straw hats agree on a secret sign to distinguish each other if shape shifter Mr 2/Bon Clay assumes their shape. We are shown them wearing a bandage on their arm but the real sign is black X drawn on the arm under the bandage, which Mr 2/Bon Clay misses when he pretends to be Usopp.
  • In Sailor Moon R DiC dub, one of the Monsters of the Week disguise themselves as Chibi-Usa's mom and calls to her using the name Small Lady. Chibi-Usa is at first fooled, happy to see her momma again, and runs to hug her. She then suddenly stops and asked the monster who they were. When the monster replies that she was her mother, Chibi-Usa say she's lying because her mother never calls her Small Lady, her royal title. In the original Japanese the monster calls her Rabbit (which is what the Dark Moon minions had been calling her), because Small Lady is part of her actual name: Usagi Small Lady Serenity.
  • In Sakura Hime Kaden, Aoba realizes that that he is being seduced by Rurijo instead of Sakura because she had lit incense, which Sakura herself hates. In addition, her scent aside from that was off; since Aoba can transform into a wolf, his sense of smell is very sensitive.
  • In Tsubasa -RESERVoir CHRoNiCLE-'s Drama CD omake, Shiritsu Horitsuba Gakuen, Kurogane figures out Yuui-sensei's real identity by literally spotting a thread on the man's shirt; Kurogane had mended a button on Fai-sensei's shirt with a different-colored thread earlier, and the impostor's shirt button was held together with thread of the original color.

    Comic Books 
  • In the Batman crossover No Man's Land, Gotham City is hit with a cataclysmic earthquake and quarantined. Batman is in the city trying to clean it up, having sent Superman away. But Superman has come back as Clark Kent, trying to help people on a different scale. He tells Batman that he did his best to rough up his clothes so as not to stand out and asks Batman how he did. Batman looks him over and says "The toes of your shoes are scuffed, but you forgot to scuff the heels. Your shirt is dirty but bears no evidence of sweat or epidermal oil secretion stains. And no one around here has smelled of deodorant, soap or laundry detergent for over five months." Clark asks how he looks to someone who isn't the world's greatest detective. Batman says he looks fine.
  • Previously in the inaugural arc of Grant Morrison's JLA, Batman deduces the true nature of the Hyperclan this way. Strength, speed, shapeshifting, aversion of fire: They're Martians. They got away with it as long as they did with each one emphasizing a different power from the common power set.
  • In one The Brave and the Bold issue, the Penguin captures Black Canary and has a female assassin impersonate her in order to kill Batman. Batman quickly subdues the impostor after noticing that she's a natural blonde, unlike the real Black Canary, who wears a wig.
  • The Spider-Man villain Chameleon is caught out like this twice when he goes after Mary Jane and Aunt May, both of whom are easily able to tell that he's not the real Peter Parker through clues like this, and are thus able to administer particularly awesome kickings of his ass as a result.
    Aunt May: You'll be interested to learn that Peter's Uncle Ben couldn't go to sleep without making sure that every door in the house was locked and double-locked. And that Peter's favorite cookies are ginger snaps and that he hates oatmeal raisin (yes, even mine).
    (Chameleon ends up passing out from the pills May had crushed into the cookies as a result of this)
  • Deadpool got a memory/flashback version in Cable & Deadpool-when T-Ray showed Deadpool the moment when Deadpool "tried to kill him and then stole his identity" in an earlier series, Deadpool was already in costume. When Cable fixed Deadpool's memories later, Deadpool remembered that he only got the costume after Weapon X, which he only joined because his cancer made him leave the army-
    Deadpool: Which I signed up for as Wade Winston Wilson!
  • The Twelve: When the group of superheroes who've been in suspended animation since 1945 thanks to a Nazi booby-trap are revived, the government goes to great lengths to make them think it's still the 1940's, wanting to break the news to them gently. The Phantom Reporter begins to notice many things that are odd. One of them is that his nurse only wears one pair or earrings, but has piercings running up her earlobes for many more.
  • In one comic, Tintin disguised himself, but failed to disguise his dog.
  • Lucky Luke: in the comic "The Singing Wire", Lucky Luke finds out that the Indian in their team is in fact not a real Indian but a disguised crook who had been sabotaging their attempts to build a telegraph wire, because he smells like shaving cream and Indians don't have beards.
  • G.I. Joe villain Zartan uses several different methods to make himself into the perfect infiltrator, but is prone to missing details. Storm Shadow foils one disguise—a moped-riding priest—by recalling how Zartan drives motorcycles.
  • When trapped in a Lotus-Eater Machine in the second story-arc of My Little Pony: Friendship is Magic (IDW), Spike realizes it's not real when Rarity tells him to forget everyone else and serve only her, and doesn't fully appreciate the significance of the Fire Ruby he brought with him (it was previously a gift he gave to her).
  • In Udon's Street Fighter II series, Guile compliments his secretary Gibson on her new contact lenses. When Gibson becomes confused by this statement, he mentions that she usually wears glasses. Later on, its revealed that the woman he was talking to was actually Juni, one of M. Bison's agents, and that the real Gibson was left Bound and Gagged in her own kitchen.
  • In the Pre-Crisis Superman comics, a Kryptonian criminal called Roz-Em had plastic surgery to make him look like Jor-El. In an "Adventure Comics" issue, he pretends to be Jor-El's ghost to drive Supergirl out of her mind. He gives himself away when he tells he knows her secret identity. Since her uncle can't know that because he died long before she was born, Supergirl deduces the "ghost's" real identity.
  • In Dead No More: The Clone Conspiracy, we're met with Gwen Stacy as part of the clones, someone who doesn't set off Spider-Man's Spider-Sense. Ultimately, the cloned Captain George Stacy notices something's off and pulls a gun on Gwen. Turns out it's not the 616 Gwen, but a disguised Spider-Gwen.
  • In Mighty Morphin' Power Rangers: Shattered Grid, in a case of Once More, with Clarity!, Lord Drakkon finally gets in contact with Ranger Slayer, who was accidentally sent into the past of the original Power Rangers team. As they talk, Finster 5 notices something - she's morphed, but she's missing her bow. It clues Drakkon in that her Brainwashed and Crazy spell is broken.
  • In one of the House of M tie-in series, Professor Xavier and Magneto become friends fighting for mutant equality. Xavier sees Magneto talking to Quicksilver, Polaris and Wanda (the latter powerless in this reality). After they leave, Xavier dryly says that "if you don't want them to know you're their father, you shouldn't dote on them so." When Magneto accuses Xavier of reading his mind, Xavier replies there was no need. "Pietro looks just like you, Lorna has your powers and Wanda bears a striking resemblance to the woman in the portrait who I presume was your wife."
  • Archie Comics' Sonic the Hedgehog: Mammoth Mogul orchestrates a fight between the Chaotix and the Freedom Fighters by disguising his own minions as one group to attack the other. The heroes manage to work out the deception from a few clues. First, "Archimedes" was able to perform one of his "teleports" at a distance while he had always before needed to be able to touch people to do it. Second, "Bunnie" was able to throw boulders with both her arms when in reality she can only do it with her cybernetic one. Third, Mogul wasn't able to properly replicate Sonic's speed and the duplicate was too slow. Fourth, Mogul only had four minions on staff to disguise while the Chaotix had six members and the Freedom Fighters had seven. Only having four of the six or seven members attacking was too suspiscious.
  • Mickey Mouse Comic Universe:
    • Used in an old Italian story. Mickey Mouse wakes up and finds himself to be an old man, residing in a run-down version of his home. An elderly Goofy claims that Mickey is suffering from amnesia and has forgotten entire decades of his life. He offers information on what happened with Mickey's former fiancée Minnie and former friends. It all seems very convincing. During a conversation between the two old men, Mickey namedrops a number of characters and observes Goofy's reaction. He then unmasks "Goofy" as an impostor and reveals that the whole tale was an elaborate hoax. The impostor failed to notice that at least one of the people Mickey mentioned in their conversation never existed (it was a made-up name), and the impostor offered to contact her. The real Goofy would be at least surprised.
    • Used it a 1990s story where someone impersonates the Phantom Blot. While investigating this Blot's crimes, Mickey is puzzled why the Blot has reverted to using long-abandoned methods from the early days of his career. Following several clues that this Blot is an immature rookie, Mickey reveals his identity as that of a college student who had done extensive research on the real Blot for a criminology course. The impostor had decided to become a copycat super-villain, but was using outdated sources on the Blot's methods, and had no real experience in orchestating crimes.
  • Wonder Woman (Rebirth): On meeting the Amazons again, Steve Trevor tries looking for the one that healed him the first time he crashed on their island. It's when the Amazons have no idea who he's talking about that Steve and Diana figure they're fakes.
  • In the Mark Millar series Prodigy, super-genius Edison Crane is approached by CIA agent Rachel Straks who needs his help against a mysterious conspiracy. Crane is able to work out a massive code being used by the sinister Tinker to pave the way for an army from another dimension to invade Earth. At which point, Rachel turns out to be Tinker's half-sister and they were using Crane to crack the code for them. They implement it...and it ends up giving Crane total control of their systems so he can thwart the entire invasion plan. Crane states that, contrary to what the duo believed, he was quick to figure out "Rachel Straks" was an anagram for "Charles Trask," the traitor from East of Eden. He also recognized that the name of the general who supposedly sent Rachel on her mission was "Bear Thriftbank" which was an anagram for Frank the Rabbit, the Imaginary Friend from Donnie Darko. Also, while Rachel's fake background was excellent, she couldn't speak Bedouin when it was a prerequisite for any CIA agent in the area she claimed to have been stationed in. "If she was lying about that, she was lying about everything else." He lampshades how their attempt to be Too Clever by Half just gave away their scheme for him.
  • The Transformers: More Than Meets the Eye: Spoofed when Nightbeat dramatically bursts in to stop Swerve hosting auditions for new crew-members to reveal it's a big fake. The things he's pointing out are blatantly obvious, starting with the idea that Swerve is being allowed to screen crewmembers at all. Also, the crudely drawn sign saying "crewditions".
  • Ultimate X-Men: Mid-way through a conversation, Charles Xavier reveals to Betsy Braddock he knows she's actually possessed by his son, David. David asks how he figured it out, and Charles notes that the upper-class Englishwoman ordering a cheeseburger and fries was a tip-off, but the fact she kept checking out the waitress's ass cinched it. The perils of being possessed by a teenaged boy.
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    Fan Works 
  • During an escape in Of Slaves and Sorrow, Arthur realizes Merlin was replaced with an enemy's illusion when Merlin addresses him as "your highness" and "your majesty" with complete sincerity.
  • Friendship Is Aura: Lucario is able to deduce that "Celestia" is an impostor (actually Chrysalis) by pointing out that she doesn't know who he is when she should, doesn't know the names of her own Guards despite socializing with them, doesn't know about her own diary (which he found earlier), and most importantly, doesn't know the nickname she and Luna called her mother.
  • In The Big Reveal, Tony thinks there's something off about Colin Morgan when he starts constantly speaking with an English accent when his normal one is Irish. He eventually suspects Colin's a different person when he asks for meat and cheese for dinner when he's supposed to be vegetarian and lactose intolerant.
  • In Diaries of a Madman, readers themselves have to do this in order to realise Discord is lying to them and an Unreliable Narrator.
  • In Dirty Sympathy Phoenix realizes that Shadi Enigmar's death by bludgeoning is too spontaneous and physical for Kristoph to have done it as Kristoph is a very patient poisoner.
  • In The Fifth Act, Genesis realizes that Cloud's story of being the younger Cloud's paternal uncle has one flaw in it: the older Cloud and younger Cloud have the same surname, when Strife is Cloud's mother's surname.
  • In His Shoes has Iroh realize that someone else has taken over Zuko's body when he isn't even tempted to join Azula and regain his honor. He's wrong about who it really is though- Iroh believes it's some kind of spirit that took over when Zuko died earlier in the story. Zuko and Sokka are actually in the middle of a "Freaky Friday" Flip.
  • Hope of the Shield Hero: Ren Amaki, unlike in canon, doesn't believe Myne's False Rape Accusation against Naofumi because he saw her get into bed with Motoyasu not long after the accusation, and on the very same night Naofumi fled. Ren had known a real victim of sexual assault in his old life, so he could tell right away that Myne is not even acting like someone who had almost been raped.
  • Rosario Vampire: Brightest Darkness Act I: In chapter 30, after their Divide and Conquer tactics work, Rarosun and Surason decide to give Rason and Dark the final push to kill each other by morphing into Mizore and Kurumu and egging them on to do so. Unfortunately for them, by that point, Mizore has been marked as Dark's soul mate, and Rason can sense his bond with Kurumu, thus easily allowing the boys to see through their disguises and realize they had been tricked.
  • Shadow of the Dragon: In chapter 16, the ghost of Reiko Ichimai is turned into a corporeal duplicate of Sakura by the Big Bad, and promptly uses the opportunity to have sex with as many people as possible to destroy Sakura's reputation. One of said boys, Renji, who was one of Reiko's one-night stands in life, knew enough about Reiko to realize it was her: as he puts it, Sakura doesn't play with her hair, insult people, or speak crudely, and couldn't have known the room they did it in was private, all of which Reiko did.
  • Peace Forged in Fire has the Tal'Shiar try to screw up peace talks between the Romulan Republic and Romulan Star Empire with a pair of False Flag Operations.
    • In the first case, they use Republic IFF beacons while attacking an Imperial warbird. One of the ships they masquerade as was destroyed months earlier.
    • In the second case, they use Republic IFF beacons while attacking the talks directly. They're spotted early because the Republic high command sent out an IFF update in response to the previous attempt.
  • In "Wayne Manor", part of the Sorrowful and Immaculate Hearts series, Thomas Wayne hires a new butler, Alfred Pennyworth, who is actually a law-enforcement plant as part of an operation against Gotham City's organized crime families. Martha Wayne immediately spots him as not who he claims to be, because no self-respecting butler would tie his tie the way Alfred does. (She goes on to say that this wasn't the only thing that gave him away, but it's the one she chooses to lead with.)
  • In The Very Secret Diary, what finally gets Ginny to distrust Tom is when she realizes that one of his many fabricated stories about his past that he's been telling her couldn't have possibly happened when he said it did, due to the timeline of his story and the one of Myrtle's life not matching up. When she realizes this, Ginny also looks into some other details in his story, and the whole thing immediately begins to fall apart.
  • The titular character in Diethard Takes a Level in Badass quickly spots and points out to others the flaw in Ohgi's testimony about Zero's Mind Control powers: Ohgi got his information from Viletta. Viletta who works for the in-universe equivalent of the NSA and is a former member of the Purist faction while Ohgi, whom she claims to love, is the Second in Command of the Black Knights, the only military power that can oppose Britannia. In other words, she has every imaginable reason to be lying.
    • Tohdoh points out another when Cornelia insists that Euphemia would never order a massacre if she hadn't been mind controlled. Tohdoh sarcastically demands if Zero mind controlled her into ordering the massacre at Saitama, or if he made Clovis purge Shinjuku, or if the Emperor conquered Japan on Zero's orders. The Britannian royal family never had a problem massacring innocent Japanese before, so why should they believe that Euphemia did.
  • In The Vain Rose's Garden Keiichi quickly realizes the orgy he apparently walked in on is fake because whoever is behind it got Urd's and Peorth's pubic hair wrong. Furthermore when he interrupts them, everyone present has identical looks of shock on their face, regardless of their personality.
  • In Bring Me Back Home, while questioning Marinette (actually her parallel universe double Bridgette) about her sudden and unexplained dislike of Chat Noir, Adrien notices that her pigtails are suddenly much longer than they were the day before. It remains to be seen just what he deduces from this information.
  • In Sword Art Online Abridged, Kirito realizes that the game's lead developer is masquerading as a player on the clearing team when he angrily shouts "Oh, so NOW you've seen TRON?!". The "now" part of that connects him to an earlier statement by the developer in episode 1, who asked if anyone has seen TRON, and was disappointed that no one appeared to.
  • A rejected student of Izumi's kidnaps Edward for revenge in Scare Tactics and threatens to slit his throat with a knife. Izumi scoffs, and lets him know that the real Edward has an automail right arm, not a left one (the villain specializes in creating humanoid dolls, and when trying to make a copy of Edward, made a reflection by mistake).
  • Prodigal Son: The road Astrid takes to discovering the truth behind Hiccup's disappearance starts when one of her students notices the illustrations and notes Hiccup took on the Night Fury in the Book of Dragons.
  • In Chrysalis Visits The Hague, former UN employee Edith realizes almost immediately that the so-called UN official she meets in the changeling hive isn't one. He has a rank that doesn't exist in the UN, has a surname that isn't a surname, can't pronounce the UN's full name correctly, doesn't know the full name of (Edith's home country) Bosnia and Herzegovina, and even is under the impression that the place is another kingdom. But what really seems to give it away for Edith is when he offers her a glass of vodka with a bread slice on top (a sort of thing done in Russia to honour the dead). Lastly, he tries to pass off a bottle cap as an order of merit.
  • In Bequeathed from Pale Estates, Ned Stark, in an uncanny show of Genre Savvy, did everything he could to prevent this, by discouraging and then outright ending his daughter Lyarra's musical studies at the expense of her happiness. Ultimately, he failed — Monford Velaryon only has to hear Lyarra sing once to realize that she isn't Ned's daughter, but Rhaegar's, and Varys soon figures it out himself after seeing Monford's reaction. Lucky for both Ned and Lyarra, they're Targaryen loyalists who intend to place the latter on the Iron Throne, so the secret is kept for the time being.
  • In Cross Cases, Dean and Castiel pay a visit to the Carpenter house to try and find Sam, and Murphy answers the door. Dean uses his usual FBI agent impersonation schtick, and Murphy- who has met and worked with actual FBI agents several times -plays along for a bit before going, "A case? Wow, you do almost sound like a Fed." He denies it, and she replies that he looks an awful lot like a Winchester, having seen the photo of him that Sam keeps in his wallet.
  • In Welcome to the Club, Natasha Romanoff quickly understands Daredevil is a Handicapped Badass when he walks on her doing yoga almost nude and has no reaction whatsoever.
  • Code Geass: Paladins of Voltron: During Reunion Over The Pacific, Kallen's the only one to notice that Suzaku referred to the Lancelot by name, even though he logically has no reason to know that.
  • My Hero School Adventure Is All Wrong As Expected: When Hachiman bumps into a student in the General education course during lunch at U.A. High School, he doesn't think anything of it until he notices that the student's posture seems to be a little off and that the guy seems a little familiar. When Totsuka tells him that the student's Quirk allows him to play music however, Hachiman remembers that he had bumped into the student before only last time he didn't have a disguise Quirk.
  • In ''Arrowverse: Leagues, Sara (offpage) points something out to Barry: during Black Siren's rampage across Central City, she could targeted apartment buildings full of sleeping families, but she chose to destroy a mostly empty lab. Why? Barry catches on, and asks more questions. The answer? She's a deep cover A.R.G.U.S. agent.
  • A Diplomatic Visit: Cozy Glow's deception is exposed in chapter 10 of Diplomacy Through Schooling when Twilight examines her magical signature and realizes it's for a pony much older than she appears to be.
  • Doctor Ghemor I Presume has Bashir being abducted and gaslighted to believe his entire life was a fabrication. After being freed, not only does the doctor make no effort whatsoever to seek his human parents and reassure himself of their existence, he fully embraces his (unwitting but still) kidnapper as a father and is nothing but a perfectly devoted son towards him. Said events allow Garak to understand that something is very, very wrong in the Bashir family if Julian is so eager to jump ship.

    Film — Animated 
  • Incredibles 2: Elastigirl twigs on to something being wrong with her infiltration of the Screenslaver's lair when she wonders why the Screenslaver, who obviously had access to a lot of resources, only used mundane deadbolt locks on his door. She then realizes that the Screenslaver she fought was a fake when she figures out that the heavy goggles he was wearing could serve as the screens for the Screenslaver to control him.
  • Megamind:
    • In the climactic battle, Titan realizes that Metroman is actually Megamind in disguise due to the distinctive way he mispronounces Metro City.
    • Although it serves as Five-Second Foreshadowing, Roxanne realises that Metroman's hideout can't be as abandoned as it seems because there's still a drink with unmelted ice on the side.
  • In The Road to El Dorado, the two con-men protagonists convince the natives of El Dorado that they are gods in human form. However, the high priest Tzekal-Kan realises the truth when he sees that Miguel has a bleeding cut from playing ball (think full-contact Mayincatec basketball) against a team of natives.
    Tzekal-Kan: Do you know why the gods demand blood sacrifices? Because gods don't bleed.
  • Wreck-It Ralph: Ralph realizes that something suspicious is going on in Sugar Rush when he notices that there’s a picture of Vanellope on the game’s boxart, contrary to King Candy’s claim that she’s a glitch character that was never supposed to be in the game.
  • Rango has to use a Snowball Lie to bluff his way out of one of these, when he claims to have killed the Jenkins brothers with one bullet and is immediately asked "All seven of them?
  • Batman: Assault on Arkham: Batman, suspecting that Harley Quinn deliberately let herself get captured, takes a look at Arkham security camera feeds. He recognizes guards who shouldn't be there that night and realizes that he's seeing recorded footage from the previous day.

    Film — Live-Action 
  • In Attack of the Killer Tomatoes!, "Master of Disguise" Sam Smith blows his cover after infiltrating the tomato camp, by asking for ketchup to put on the arm he's about to eat.
  • A Beautiful Mind: a variation: this is how John Nash finally realizes his chronic hallucinations. One of his hallucinations is a young girl, but even though he's seen her for years, she's never grown any older.
  • In Big Eyes, when Margaret finds a shipping box of paintings by S. Cenic in the closet, which helps her realize that Walter had been lying about painting in Paris.
  • The point of the Voight-Kampff Test in Blade Runner is to spot the thread for Replicants. Replicants are biological androids completely identical to humans down to blood, sweat and bad breath, but they have no empathy. The test involves asking questions that would provoke an empathetic response in a human and note when the replicant fails to show any physical signs.
  • In the documentary Catfish, Nev begins to realize Megan is not real because he finds out she took other people's songs and said they were hers.
  • The Da Vinci Code: zigzagged. Bank manager Andre Vernet is helping the protagonists flee the police by putting them in a truck and pretending to be the driver. A detective, though, notices a Rolex on his hand and wonders how a truck driver can afford it. Without skipping a beat, Vernet convincingly plays it off as a fake he bought from some shady dealer and even offers to sell it to the cop for cheap.
  • Delta Force 2: The Colombian Connection has a US Agent able to get close to the Big Bad, Ramon Cota, and become his second in command. However, he gives himself up when he sets up Cota's arrest during his flight on a private jet, because he was the only person Cota told about it.
  • In Die Hard 2: Die Harder, McClane notices two men sitting at a table who, despite being dressed in business casual attire, are wearing combat boots rather than appropriate shoes. Becoming suspicious he follows them, reports, them, discovers they are Mooks of the Big Bad who are up to no good, and does everything in his power to foil them, which would have worked without a hitch if the cops in the airport weren't such belligerent, incompetent assholes.
  • In Die Hard with a Vengeance, McClane gets in an elevator with several terrorists disguised as cops and security. He notices they're using terminology incorrectly, referring to the elevator as a "lift" (a European/British term) and a weather report as raining "dogs and cats" (instead of "cats and dogs"). McClane is visibly suspicious, and spots that "Detective Otto" is wearing a police badge that belongs to a friend of his. He assesses whether anyone in the elevator is a real cop by asking what the lottery numbers were last night, since it's been established that all New York cops play the lottery. When no one knows, McClane realizes that they're all imposters.
  • In Double Indemnity Keyes is entirely satisfied that the late Mr. Dietrichson's death was not suspicious and entirely accidental... until he realizes that the man had broken his leg right after signing up for a generous accident coverage policy, yet he didn't file a claim for his leg. This is the first piece of evidence that Dietrichson didn't even know about the policy in question.
  • Dredd:
    • Judge Dredd trips up a corrupt Judge on Ma-Ma's payroll this way. When the Judge states that he was responding to a call for backup, Dredd points out that the Judge didn't ask about the rookie Anderson; Dredd was alone in hostile territory at the time, and a Judge really responding to such a call for Dredd and Anderson would have have asked where the missing rookie was.
    • The same thing happens with the rookie herself. The corrupt woman Judge of the group sent by Ma-Ma claims she will kill the rookie, because as a Judge, Anderson is likely to trust her and hesitate. Anderson, being psychic, sees through the deception almost immediately and kills the corrupt judge after a brief exchange.
  • Get Smart: Max spots the traitor because, after visiting the Big Bad's destroyed lair and declaring all the uranium supplies had already gone, the traitor sets off the Geiger counter concealed in Max's watch. On mentioning this he then spots that the traitor's stab wound is freshly bleeding, as if nerves of being detected were prompting a higher blood flow.
  • In Ghost Ship, Epps catches on that the villain has killed and impersonated her last remaining crewmate when he doesn't ask her what happened to the second-to-last one, who's been killed in the interim. He drops the act and admits he already knows because he killed the other one too.
  • The climax of The Godfather Part II is a famous example. During a meeting in a Havana nightclub, Michael introduces Hyman Roth's lieutenant Johnny Ola to his brother Fredo, and Fredo casually says "We haven't met." A few moments later, while the guys are gushing over a lurid live show at the club, Fredo gets excited and accidentally mentions that he took Johnny to see the show a few days previously. Turns out that Fredo and Johnny have met before, but Fredo lied and claimed that they hadn't. From this tiny slip-up, Michael is able to figure out that Fredo has betrayed the family, and is working with Hyman Roth to bring him down.
  • In Godzilla (2014), after breaking back into old Janjira, after it was quarantined due to a reactor meltdown, Joe Brody realizes the place isn't radioactive when he spots three dogs chasing each other, when they should be dead from radiation. A quick check of his Geiger counter confirms his suspicions.
  • In the 1974 film Godzilla vs. Mechagodzilla, the human protagonists begin to suspect that the disguised Mechagodzilla is a fake when it attacks Anguirus... something the REAL Godzilla wouldn't do since he and Anguirus are allies. Their suspicions are confirmed when the original Godzilla shows up to do battle against Mechagodzilla for the first time. Anguirus also immediately notices that the disguised Mechagodzilla is a fake because it doesn't sound or act like the Godzilla he knows.
  • The Great Escape: This is how Bartlett and MacDonald are captured. A Gestapo agent asks to see their identification and asks them questions in German. When he is finished, he says "good luck" to them in English, and MacDonald blunders by replying in English. A case of Truth in Television; this is pretty much exactly how Roger Bushell (the basis for the Bartlett character) was caught in the real escape (see "Real Life").
  • In Hangmen Also Die!, Inspector Gruber figures out that Dr. Svoboda and Mascha weren't actually having an affair when he sees lipstick smeared on his own cheek in the mirror, recalling that the lipstick mark on Dr. Svoboda's cheek was immaculate and thus deducing that it must have been placed there intentionally to throw him off their scent by making it seem like what they were up to was having an affair.
  • Harry Potter:
    • In Harry Potter and the Chamber of Secrets, Harry and Ron's plan to disguise themselves as Crabbe and Goyle is nearly undone at the start when Malfoy notices "Goyle" wearing glasses. When Harry gives the excuse he was reading, Malfoy's response is "READING?!......I didn't know you could read."note 
    • Harry Potter and the Goblet of Fire: Barty Crouch Jr. used a Polyjuice potion to disguise himself as Mad-eye Moody. However, Barty Crouch Sr. spotted "Moody" doing Junior's signature tongue-flick, which gave him away. Note this was only done in the film version.
  • This is a plot point in The Hateful Eight, as soon as Major Marquis Warren arrives at Minny's Haberdashery he immediately notices that things are wrong. For example: a single jelly bean is lying on the ground far away from its storage jar, visitors are wearing hats inside (which the rules of the haberdashery don't allow), Minny is said to be on vacation (a flimsy story), Minny's famous stew is still fresh despite the fact that she's been gone for a while according to Bob, guests are sitting on Sweet Dave's chair (which would never be allowed), and Bob (a Mexican) has been hired to watch over the haberdashery while Minny is "gone" (Minny hates Mexicans so she would never do this.) His suspicions are proven to be correct.
  • In Hot Pursuit, cop Cooper and drug lord wife Daniella barely escape when masked killers shoot up a mansion. Cooper calls for help and is met at a diner by cops Dixon and Hauser who said they were responding to her call. Cooper reflects on how she only put out the call 20 minutes earlier and to arrive here from the station so fast, Dixon and Hauser would have had to have been doing 180 miles an hour. She then sees their car's fuel gauge indicating they have only traveled about 30 miles which is where the mansion was. The clincher comes when Cooper sees Hauser has the same arm tattoo as one of the masked gunmen.
  • In Inception there's an example of literally spotting the thread, when Saito notices that the carpet in a room he's in is made of the wrong fibre, tipping him off that he's still in a dream.
  • Inglourious Basterds, Deiter Hellstrom notes that the Inglourious Basterds pretending to be German officers are behaving strangely. He also says that Lieutenant Hicox's German accent sounds strange. Hicox covers for himself by saying that he's from a small Swiss mountain village with a unique regional accent. This seems to quell Hellstrom's suspicions, but then he asks for three drinks with the wrong hand gesture, using "index-middle-ring" and not "thumb-index-middle", as Germans usually do it. This finally convinces Hellstrom that he's an impostor.
  • The Italian Job (2003) has this: Steve realizes Stella is John's daughter because of a phrase she uses, that he's never heard from anyone one else but John.
    Steve: Still don't trust me?
    Stella: I trust everyone. I just don't trust the devil inside them.
  • In The Last Witch Hunter, Kaulder has a penchant for spotting those.
    • He realizes that something's sketchy about 36th Dolan's demise when he notes that retirony is normally not Truth in Television.
    • The illusion that 36th Dolan's house is neatly cleaned up is shattered when he notices a Plague Fly - a dead-ringer for Dark Magic - dead on the floor of a house which was locked up for the entire day. When he tests the house for Black Magic because of it, Glamour Failure ensues.
    • His clue to Ellic being part of a gang rather than singular assassin is the fact that Ellic is too low-level a warlock to perform shapeshifting Kaulder's seen him wear.
  • Marvel Cinematic Universe:
    • Captain America: The First Avenger:
      • Steve Rogers wakes up in a 1940s-era room. A woman wearing a period-specific military uniform enters to greet him. Rogers catches on that something is amiss when he remembers being at a baseball game that was seemingly broadcast live over a radio in the same room.
      • In a meta example, viewers familiar with 1940s period fashion can tell the scene is in the present and not a dream because the agent is wearing a bra that isn't noticeable through her shirt. Also, while her hair is curly (as was the style in the 1940s), the curls are much too small and haphazard to be true Victory Curls. Steve seems to notice from the second he sees her.
    • Captain America: The Winter Soldier:
      • Steve notices an ammo bunker at what's left of the decommissioned Camp Lehigh that's way too close to the barracks for either safety or Army regulations. It turns out to be the secret base holding Zola's uploaded brain.
      • Earlier in the film Steve realises the friends and colleagues piling into the elevator with him on apparently innocent business are there to attack or restrain him because he spots the tell-tale signs of nervousness and weapon-readiness they are trying to conceal. Being Steve Rogers, he gives away the element of surprise by asking if anyone wants to opt out of the coming fight.
    • Captain Marvel:
      • After lecturing Carol that everyone calls him Fury, and absolutely no-one calls him anything else, Fury is on high alert when another agent calls him "Nicholas". Carol is also able to track another Skrull onto a train when they assume the form of an old woman... whom Carol had run into by accident getting off of the train just before getting on the train herself.
      • A double-whammy when Yon-Rogg confronts Carol near the end of the movie: "Carol" answers his questions perfectly until he presses "her" for more detail and "she" slips up. This both clues him in to "Carol" being a Skrull and to "Vers" having turned on him.
  • In Mission: Impossible – Ghost Protocol, murderous thief Sabine is canny enough to know that IMF is after the intelligence she stole (killing IMF Agent Hanaway to do so), and realizes that Ethan and Brandt are IMF agents when she sees Brandt's hi-tech contact lens, which Hanaway had been wearing when she killed him at the start of the film.
  • In Our Man Flint, the protagonist reveals two fake guards that have had plastic surgery to look exactly like the regular ones. The give-away is that they wear uniform ribbons made from an existing - but unofficial - medal. Flint spots this at first glance.
  • In Paycheck, Jennings suspects that the Rachel he meets in the cafe is an impostor when he sees a colored contact lens shift out of position while they kiss.
  • The ending of Primal Fear has Martin Vail realize something is off when his client, Aaron, said "I hope her neck is okay." The injury he refers to happened during an attack made by his split-personality, during which Aaron allegedly has no memory - and yet he apparently knew about where "Roy" had attacked the prosecutor.
  • In Quantum of Solace, M suspects that the CIA is running an operation in Bolivia, so she calls their head office and asks about it. She's routed to the CIA section chief for South America, who denies running any operations in Bolivia. M immediately concludes that he's lying because if there really weren't any operations in the country, she wouldn't have been routed so high up the chain.
  • In Rags, Lloyd manages to discover that Charlie is Rags by noticing a conspicuous signature on Rags' shoes, which matches the one on Charlie's.
  • Zigzagged in Scream (1996): Billy Loomis, who has been suspected of being the killer for the entire movie, and even taken into custody at one point (although he was later cleared) is asked by his girlfriend Sidney who he called with his "One Phone Call" when he was arrested. He tells her that he called his father, but Sidney points out that the station called his father. Not thirty seconds later, he is killed, exonerating him from suspicion. However, it turns out that he actually was the killer (or one of them anyway) and had faked his death, and the thread Sidney had spotted earlier was probably correct.
  • This happens at near the end of Scream 4. After it seems like the latest Ghostface Sidney's cousin, Jill, got away with the perfect crime in murdering Sidney, and replacing her as the Final Girl, she makes a fatal mistake. She tells Dewey about her arm injury pointing out how it was the same injury Gale Weathers had. When Dewey mentioned this to his on-again, off-again life mate, she points out that Jill could only have gotten the same injury if she was the Ghostface who attacked her at the annual Stab party. Before they can expose Jill, Sidney fights and kills her after Jill found out she was still alive and tried to finish the job.
  • In Sherlock Holmes: A Game of Shadows, Holmes and Watson find which of the ambassadors at the peace summit has been replaced by an impostor when Watson deliberately knocks a tray of glasses over. The fake is the only one who doesn't turn and look, being too enveloped in his role to produce a spontaneous reaction.
  • in Stalag 17, the Germans have planted a spy, Price, in a POW camp posing as an American flier from Cleveland. Sefton (William Holden) suspects the ruse, and in the climactic scene confronts Price:
    Sefton: When was Pearl Harbor, Price, or don't you know that?
    Price: December 7th, '41.
    Sefton: What time?
    Price: 6:00. I was having dinner.
    Sefton: 6:00 in Berlin. [To the other barrack members:] They were having lunch in Cleveland.
  • In Star Trek IV: The Voyage Home, Kirk and party are within seconds of successfully bluffing their way out of the hospital with the wounded Chekov in tow when this exchange occurs.
    Guard: How's the patient, Doctor?
    Kirk: He's going to make it.
    Guard: He? They went in with a she.
    Kirk: (to himself) One little mistake... [they run]
  • In Star Trek V: The Final Frontier, Kirk finds something off in "God's" demands for his followers:
    "God": This... starship... could it carry my... wisdom beyond the Barrier?
    Sybok: It could! Yes!
    "God": Then I shall make use of this starship.
    Sybok: It will be your chariot!
    Kirk: Excuse me...
    "God": It will carry my power through every corner of Creation...
    Kirk: Excuse me, I'd just like to ask a question... What does God need with a Starship?
  • The dramatic thrust of Sucker Punch is almost entirely dependent on whether or not the audience can do this. There's a really big clue, though, just before The Reveal that a twist is coming because a character's wearing a dress she shouldn't have.
  • The James Bond film Tomorrow Never Dies features the Big Bad's tech assistant Gupta immediately uncovering Bond's secret identity. The tech calls it "Gupta's Law of Creative Anomaly", and explains that anyone's personnel record is bound to have errors and flaws. Bond's fake banker profile is too perfect, meaning he's obviously a government agent.
  • The ending of the 1974 version of The Taking of Pelham One Two Three has the last remaining hijacker accidentally giving away his identity with his recognizable sneeze.
  • In Transformers: Age of Extinction, when Cade is trying to deny any knowledge of Optimus Prime to the CIA, he refers to Optimus as "he", alerting Attinger that Cade must have spoken to Optimus if he was using gender-pronouns. Flimsy evidence, but they ain't exactly worried about due process.
  • In The Truman Show, the world Truman spent his entire life in starts collapsing as he begins noticing multiple threads pulling apart.
    • In particular, there's a point where he observes that a lady on a red bike, a man with flowers, and a vintage Volkswagen beetle with a dented fender, go around the block, over and over again, and always in the exact same order at the exact same time.
    • During the "Nuclear Meltdown" encountered during his escape attempt, his reaction to a police officer uttering "You're welcome, Truman." without ever asking his name or being shown any ID.
    • The writers handwave the falling spotlight as a falling piece of a random satellite, but that's a pretty blatant lie for us.
    • One day when Truman is driving into work, his radio starts picking up interference and he notices that it's narrating everything he's doing (which the radio show host handwaves as being interference from a police scanner).
    • During a heated argument with Meryl which ends with him holding a kitchen gadget to her neck, she yells "do something" at the camera.
    • While looking at his wedding album, he notices a photo showing Meryl doing a Lying Finger Cross.
    • In a deleted scene, Truman gives his sandwich to a man in a wheelchair, and two days later he notices the same man jogging like he's in perfect health. He's even wearing the same shoes.
    • To the audience, the town Truman is living in is obviously fake looking but Truman grew up in that setting so to him all the oddities look perfectly normal. However, the cost of maintaining an entire fake town would be enormous and it's clear that the producers have been Cutting Corners. Sets are reused, same extras are used for multiple roles and continuity is not adhered to. Truman has been basically brainwashed to accept everything that is happening as normal and not to question things that are out of place, but the anomalies are allowed to get so out of control that even Truman realizes that things are massively wrong in his life.
  • In Truth, bloggers examine memos used in support of a 60Minutes broadcast and find out that the memos, allegedly typed in the 1970s, could be reproduced perfectly with the default settings of Microsoft Word, and early 1970s machines that could have produced the memos would not have been available to the alleged author.
  • In WarCraft, Khadgar realizes that something doesn't add up in Medivh's behaviour when the latter burns down his research on the Portal.
  • In Wild Wild West, Jim West immediately recognizes that Artemis Gordon is not the real President Grant (he was basically practicing his decoy costume). When Gordon asks what the tipoff was, West points out his class ring — it identifies him as a Harvard graduate, and the President attended West Point. Of course, there's a very good reason why the make-up was so good - Grant and Gordon are played by the same actor.
  • In Wishmaster, Alex eventually catches on that the Djinn disguised himself as one of her friends. The Djinn manages to explain a Saying Too Much slip-up, but his antagonistic behavior and constant offers to do something for her (thereby invoking a wish) give him away.
  • In X2: X-Men United, Wolverine figures out Mystique isn't Jean because she has the scars where he stabbed her in the previous movie. Later in the same movie, Stryker takes one look at Mystique from across a large room and knows she's not Wolverine simply saying "I know my own work".
  • xXx:
    • Xander Cage spotting the fake diner hold-up and critiquing everyone in on it due to all the dangling threads he spotted within a minute:
      Xander: You know, you almost had me going there for a while. I was a bit groggy before, then I started noticing things. Like, you got a stockbroker over here, all dressed up, reading the Financial Times on a Sunday morning when the market's closed. Unlikely, but okay, I can go with that. I can even go with the stick-up man packing a cop-issue Beretta. But you want to know where you blew it? With her. [points to the waitress] My aunt was in the restaurant business all her life. There's no way in hell a career waitress comes to work in high heels. She'd have blisters the size of pancakes before lunch. And if she ain't real, then this whole thing ain't real. That's how I knew this bozo over here wouldn't get a shot off even if we waited till St. Patrick's Day. Because there's nothing but blanks in these guns. Oh, and no offense, but their performances were terrible.
    • Subverted in the next scene when Xander assumes they are still playing with him after dumping him in Columbian drug cartel territory. He figures it out just before Danny Trejo goes to work on him with a machete.
    • In the sequel, Xander is at a market square when a man comes up, strikes up a talk and leaves a bag behind. Xander looks in to find a ticking bomb seconds before a SWAT team runs in to arrest him. Rolling his eyes, Xander takes down a cop and spins around, firing his machine gun, showing it's full of blanks. He relates how he knew it was a test: A teen is listening to expensive headphones rather than the cheaper knock-offs; a woman is running to catch a bus that won't leave for two hours; a "cop" is paying for a drink with foreign currency; and the old man struck up a talk somehow knowing Xander spoke English.
  • You Only Live Twice. Blofeld sees through Bond's astronaut disguise when he attempts to enter the capsule while carrying his air conditioner unit in his hand, something a real astronaut would never do.

    Literature 
  • The Adventures of Huckleberry Finn: Huck goes in disguise as a girl at one point; the woman he's talking to gets suspicious when he attempts to thread a needle by putting the needle onto the thread, whereas any girl would know that it is far easier to do it the other way around, and ultimately is found out when he catches a ball of yarn tossed to him via closing his legs such that it lands on his lap. A girl would instead open her legs to catch it on her skirt. In short, Huck didn't do his research.
  • In Animorphs, Jake winds up infested by a Yeerk after falling into a Yeerk pool. When "Jake" spots Ax (an Andalite, whose species are at war with the Yeerks), his face momentarily contorts into a look of hate, alerting everyone to the problem; the Yeerk blows it even worse when Ax touches him, at which point he yells "GET YOUR HANDS OFF ME, ANDALITE FILTH!". The other Animorphs also point out that if Jake was really the one "in the driver's seat", he would have gone along with their plan to starve the Yeerk just to make absolutely sure and settle everyone’s minds. But since the Yeerk was fighting them every step of the way, the other Animorphs locked him up, knowing with 100% surety that he was a Controller.
  • In the BattleTech novel The Sword and the Dagger, it's revealed that Hanse Davion, the First Prince of the Federated Suns, has been replaced with an impostor because the impostor can't pilot Hanse's personal Battlemaster, since the neurohelmet a mechwarrior wears to give their mech balance has to be carefully calibrated to the mechwarrior's brainwave pattern.
  • In The Book of the New Sun, Severian spots a literal thread: a ribbon sticking out from the side of the head of the mysterious soldier he battles at the Sanguinary Fields, which should tip him off that it's really Agilus in disguise. Severian spots the clue, but cannot remember where he has seen such a thing before until two chapters later, after he has almost been killed in the totally unnecessary duel. It's a tip-off to the reader. As a famously Unreliable Narrator, because he's not as clever as he appears, Severian often mentions threads, but fails to pull them. And if Severian can't unravel this clue, how can he be expected to unravel the fact that he's being manipulated by time-traveling aliens?
  • In Bulldog Drummond, Drummond is able to recognise the Comte de Guy as Peterson in disguise, though he looks completely different, because he has the same unconscious mannerism when he's feeling impatient.
  • Clive Cussler is fond of this in many of his books from Spot the Impostor to figuring out clues behind some event.
    • In Iceberg, Dirk Pitt instantly knows something is up with Kristi as she is supposed to have spent years living in the jungles of South America but her tan is far too shallow.
    • In The Mediterranean Caper, Pitt finds it odd that Bruno Von Till, who boasts of his past as a World War I combat pilot, would have a model of a submarine in his study. This leads to his investigation that Von Till is actually wanted Nazi war criminal Admiral Eric Heibert.
    • The same novel has Pitt managing to spot the clues to tell him cop Darius is The Mole for Von Till.
  • In The Oregon Files novel Skeleton Coast, Sloane Macintryre shocks Juan by being the first person to see through the Oregon's facade of a run-down tramp ship. She's spotted several of the crewmembers wearing clothing or watches far too expensive for a crew barely scraping by. Also, having grown up around boats all her life, she knows there's no way the Oregon can be moving so fast without highly advanced turbines developed after it was built. The fact the ship was moving when the bridge telegram was at "all stop" and it took several minutes for the "smokestacks" to billow out smoke added to it. The clincher is her pulling back a painting on the wall to reveal a hidden camera as she'd seen Juan glancing to it a few times during their talk.
  • In Zero Dawn, Pitt has a computer search uncover that over 80 people died on April 18th, 1906, all at almost the same time at different places but each obit almost exactly the same with just a few words changed. They all actually died in an experiment gone wrong (which inadvertently caused the San Francisco Earthquake) and the government hushed it up. Lampshaded by the government agent dryly stating that in 1906, no one was really considering the possibility some fancy machine would be able to see through the pattern.
  • The Isaac Bell series focuses on a detective who's a master of spotting the tiny details (such as figuring out a man faked being knocked out in a fight as his eyes are still very alert rather than showing the effects of a blow).
  • In Codex Alera, Magnus figures out that First Spear Valiar Marcus is actually the traitorous Cursor Fidelias by spotting a number of such threads, such as Marcus being able to reliably spot him when he's trying to be stealthy, and seemingly having disappeared off the face of Carna after serving his military term (because Fidelias abandoned that cover identity after serving his time, later reusing it to spy on the First Aleran).
  • Basically the reason the fake meteorite is exposed in Dan Brown's novel Deception Point; all the evidence supported the idea that the meteor in the iceberg was real, but once they discovered a few microscopic fish under the meteorite, introducing the idea that it had been planted in that iceberg on purpose, Rachel, Michael and Corky are able to take another look at the evidence and admit that there are other explanations for the evidence beyond it coming from outer space.
  • In Do Androids Dream of Electric Sheep?, Deckard is initially led to believe that he's registered a "false positive" on Rachel Rosen's Voight-Kampff test (ie. he's identified a real human with stunted empathy as an android, something that would have invalidated the entire testing process and forced Earth's police agencies to come up with a whole new test from scratch). The Rosens, apparently looking to protect their own reputation, try to buy his silence on the matter by bribing him with their (very rare) pet owl, but when Rachel continuously refers to the owl as "it" instead of "she", Deckard realizes he's been had: Rachel is an android, and the Rosens were trying to set him up to blackmail him into dropping his investigation.
  • In Double Star by Robert A. Heinlein, an actor is hired to double for a prominent politician who has been kidnapped, and spends weeks studying the politician's files on everyone around him to make the masquerade work. He notices that the file on the emperor is nearly empty, and assumes that they don't have much contact... until he meets the emperor, and gets found out, because why would you need files to remember how you deal with your longtime friend? He's caught when he dutifully plays with the emperor's toy trains instead of teasing him about them.
    "It was not until later that I realized that the file had not been defective, in view of the theory on which it was based, i.e. it was intended to let a famous man remember details about the less famous. But that was precisely what the Emperor was not—less famous, I mean. Of course Bonforte needed no notes..."
  • In Dale Brown's Edge of Battle, Jason tries to disguise himself as a Mexican to infiltrate a meeting by the villains, which works until one mook notices that he has a gringo's blue eyes.
  • Discussed in The Emperor's Soul by Wan ShaiLu, a Master Forger whose work requires her to be a polymath with an exacting eye for detail. When she learns that the Emperor is brain-dead and a government faction is trying to hide that fact by keeping him "in seclusion", her first instruction is that someone regularly fill the Imperial chamber pot, because servants would notice if he stopped using the toilet.
  • In the Georgette Heyer novel False Colours, Kit is caught in a Twin Switch when he opens a snuffbox the wrong way.
  • Garrett, P.I.: In Faded Steel Heat, Garrett is impersonated by a shape shifter, who visits Morley Dotes' restaurant to find out how much Garrett's friends know. The phony is exposed almost immediately, as Morley's waiters offer "Garrett" a platter of roasted green peppers, and the fake tucks into it at once. The offered platter had been a prank, as steak-loving Garrett has spent several books denigrating Dotes's vegetarian menu, and green peppers in particular. Note that they did know shape shifters were around, so it wasn't that huge leap from 'Garrett acting unusual' to suspecting it was a 'shifter. Flushing them out was actually one of the reasons for feeding him that meal.
  • In Ghost, when looking for a nuclear bomb in the press parking lot at Notre Dame, where the Pope was scheduled to speak, Mike identifies the enemy agent when he claims to be from Alabama, but is eating his meal in the Continental style (not switching the fork to the right hand to cut with a knife in the left) instead of the American one.
  • Harry Potter
    • Harry and Ron make some errors when they turn into Crabbe and Goyle in Chamber of Secrets, although Malfoy apparently doesn't think anything of it other than that his friends are acting a bit weird today. For example, they forget that they're supposed to laugh at Malfoy's jokes and Ron corrects Malfoy when he gets Percy's name wrong.
    • In Goblet of Fire, Dumbledore realized that something was up with "Moody" when he removed Harry from Dumbledore's sight—the safest place he could be—in the midst of all the chaos surrounding Cedric's death.
    • Harry Potter and the Deathly Hallows: At Fleur and Bill's wedding, Harry uses the Polyjuice Potion to disguise himself. It doesn't fool Luna Lovegood, who recognizes him from his expression.
    • A villainous example: In Hallows, the Death Eaters realize which one of the several Harrys are the real one when he uses his "signature" spell, Expelliarmus.
    • Also in Deathly Hallows, Harry, Ron and Hermione go to visit Xenophilius Lovegood in order to find out more about the Hallows. To their surprise, Lovegood is rather reluctant to talk to them, even though he had been using his magazine to support Harry. All through their meeting, Lovegood acts very strange, and it isn't until Harry goes to Luna's bedroom and notices a thick layer of dust on the furniture that he realizes Lovegood had been lying to them about Luna being down by the river in order to get them to stay put long enough for him to call the Death Eaters so they could be captured.
  • Honor Harrington:
    • In Echoes of Honor, a Haven admiral notices that the prison planet Hades has been taken over because the warden has been playing a game of chess with him (move by move, by courier ship), and the warden's move doesn't arrive when it should.
      • It's worth noting that the rest of his command staff thinks he's insane for sending a whole battle fleet to investigate on the basis of a missing chess move. He is, however, right.
    • Used deliberately when a Solarian supposedly assisting Haven's State Sec digitally alters the uniforms and bridge of the State Sec crew to look Manticoran when they communicate with an Andermani warship. The Andermani commander realizes immediately that someone is trying to con him because the Solarian secretly inserted a CGI "extra" in the background of the bridge, one that looks exactly like Honor Harrington. Not only did the commander know her personally, having met in the past, at the time she was thought dead after being executed by the People's Republic of Haven.
  • The Hunger Games: The official, "live-action" shots of District 13 are revealed to be Stock Footage by a mockingjay which flies past the screen at the exact same spot despite claims that it is filmed repeatedly every year.
  • In Into The Drowning Deep, sirens can perfectly mimic any sound they hear, but they can only repeat it exactly and have no sense of the context of the sounds most of the time. As such, they can be found out when they do things like mimic the sound of a boat motor a mile under the surface or repeat the same whale song regardless of circumstance.
  • Maximum Ride's clone might have been a more successful replacement if she had known that the blind guy was the Team Chef, but given that the flock's youngest member is a freakin' mind reader the chances are slim.
  • In the Philip K. Dick short story Precious Artefact, the reconstruction engineer first suspects on returning from Mars that the Earth streets he's seeing aren't real when his coin falls through a dispenser. This is later confirmed for him when his houseplant, in Earth's supposedly more humid environment, dies of dehydration.
  • Rivers of London: In The Hanging Tree, the sight of an expensive mechanical watch on Martin Chorley's wrist — one without microchips that can be destroyed by magic — tips Peter off that Chorley is almost certainly the Faceless Man.
  • In Santiago: A Myth of the Far Future, Cain is caught in a vision of being on his home planet by Altair of Altair. When he's asked by Altair, in the guise of a girl he had a crush on, to drop the "stick" (his gun) and help her across a brook, he shoots her and tells the corpse that his home planet doesn't have any brooks.
  • In Shaman Blues, Witkacy spots that something doesn't quite match in Tadeusz Dzwon's story by the man's brief terror at the very mention of his sister, putting the detective on fast track to figuring out the murderer.
  • Star Wars Legends: Galaxy of Fear has a spot of this in Clones. Our heroes have been separated and Tash is on the run from a number of her own clones, commanded by a literal Darth Vader Clone. When she's menaced by a clone of Hoole, she's saved by Zak, who then wants her to punch in a code to summon their ship... but then she remembers that both of them are supposed to know the code, so why hasn't he done it? Yep, he's a clone too, and goes on the attack as soon as she figures it out.
  • Agatha Christie's Tommy and Tuppence book N or M?: Tuppence does this almost literally. Her fake identity, "Mrs. Blenkensop," is not good at knitting, but Tuppence is. At one point, she gets distracted and Mrs. Blenkensop suddenly starts knitting perfectly. She tells the others who witness this that she was pretending to be a poor knitter so one of the other residents at the hotel would have an excuse to help her.
  • Tortall Universe:
    • Aly does her best to avoid mistakes of this kind in the Trickster's Duet and pretend to be a simple country maid while posing as a slave in the Copper Isles instead of the highly educated daughter of Sir Alanna, King's Champion of Tortall. This is made difficult when Sarai and Dove don't want to hear about anything but Alanna, and Dove notes every slip.
    • Beka Cooper:
      • An illegal slave sale in Terrier is found out by the spotting of several such threads in the announcement they sent out. The threads were these: They used pure red wax for seals (the legitimate version includes ebony shavings), used a cotton ribbon (legitimate announcements use silk), misnamed the king, and wrote the letter "s" normally (scribes at the Ministry of Slave Sales put an extra curl on the letter "s").
      • Bloodhound: Beka notices a man trying to exchange counterfeit silver coins for copper ones because it's too early in the evening for most Lower City residents to have silver (gambling starts later at night, and gambling is the only real way for most to get silver). When she investigates further, she notices that the profile on the coins is pointed in the wrong direction. The man is quickly caught.
  • In The Unexplored Summon://Blood-Sign, Kyousuke first suspects that Aoi is actually the White Queen when she doesn't forget about him when he's out of her sight (in the setting, normal people can't remember anything about summoners outside their field of vision). This wasn't certain evidence on its own, since Aoi is an Artificial Human to which this might not apply. The key evidence is "Aoi" using a specific technique for squirting water with one's hands, which Kyousuke originally taught to the White Queen. However, it's implied that these slip-ups may have actually been deliberate, given that the end of that novel reveals that the White Queen wanted Kyousuke to defeat her.
  • Vorkosigan Saga: Invoked at one point in Cetaganda, when the Barrayarian Embassy's "protocol officer" Colonel Vorreedi has a talk with one of the young officers sent to officially represent his homeworld at a State Funeral. With a few leading questions on both sides he swiftly sees the truth behind Miles, Lord Vorkosigan's cover as the Prime Minister's half-crippled son being given a sinecure to keep him out of everyone's hair... aside from the detail that he was not at the moment on a top secret covert ops mission at the behest of ImpSec director Simon Illyan himself.
  • Warhammer 40,000: Eisenhorn:
    Eisenhorn: You could talk like Nayl and use Glossia thanks to Jekud, but Jekud didn't know what Nayl knew. We fought Sadia on Lethe Eleven, not Eechan.
  • In The Witchlands, Cam realizes that Vivia might not be the person behind the assassination attempt on Merik when she learns that the Empress of Marstok, whose well-being doesn't interest Vivia in the slightest, has been attacked in the same way.
  • In a Russian fantasy novel Wolfhound the titular hero exposes a disguised assassin when he notices that although the man wears a distinct native costume, the patterns on his shirt and boots do not match and indicate him as a member of two different clans at the same time.
  • In Keith Laumer's Worlds of the Imperium, the protagonist is recruited as a spy because his counterpart in an alternate universe was a ruthless dictator, and the plan was to replace his double to allow for a successful revolution. The plan works and he's successful in convincing everyone he's the dictator... up until the moment, flush with how successful the masquerade has been, he stands to greet one of the dictator's confidants and is immediately exposed. No one outside the dictator's immediate circle knew he's lost the use of his legs.
  • Mistborn: The Kandra can easily shapeshift into anyone whose body they've eaten, except for their hair, which they need to transplant strand by strand. In Wax and Wayne, Wayne muses that he should keep an eye out for someone without any hair on their... arms.
  • In Outpost, Striker and Hop approach Councilman Golm during his regular lunchtime park outing. After realizing the Councilman is likely the bait, Striker looks around, initially seeing nothing out of the ordinary. Then he notices four things: there are no kids in the park, even though it's a popular place for school field trips; the two old ladies walking past them were carrying bags that looks far too heavy, and they themselves looked more muscular than their wrinkles would suggest; a young couple was sitting on the next bench over, even though lovers generally preferred to find isolated spots; and there were three blue-collar workers in a central city park, wearing coveralls, in the middle of a workday. Striker and Hop barely manage to get away, and only because of this and because Fiddler was acting as a Friendly Sniper.
  • The Alice Network: Rene realizes Eve isn't from the French region she claims based on her accent. She allays suspicions by lying that she traveled from there for work, and didn't want to say anything since that's very near the German border, thus many French people would suspect that she's a collaborator.

    Live-Action TV 

In General:

  • Soap Operas like to use this with evil twins, etc. Most of the time, the surrounding characters are completely fooled until the real person is able to escape and confront them, but a handful of story lines have averted this:
    • All My Children's Janet pretended to be her sister Natalie. Not only did Natalie's fiance Trevor already suspect this after sleeping with Janet, Janet said something that Trevor had heard Janet say previously.
      • Janet also hired an actor to play Will, Dixie's dead brother, with the intent of terrorizing Dixie. Dixie feared she was going off the deep end until another character mentioned a run-in with "Will". Suspicious, Dixie went to the cemetery (where "Will" had supposedly been haunting her) and when "Will" appeared, began interrogating him about a nursery rhyme from their childhood. Of course, he couldn't answer. To top it off, when he tried to run, he was confronted by her husband, thus proving himself to be made of flesh and blood rather than a ghost.
    • Days of Our Lives' Hope was replaced by the evil princess Gina, but her son and husband suspected this immediately, as Gina's demeanor was icy and cruel, in stark contrast to Hope's.
    • General Hospital, Mac was replaced by a double who imitated him a little too perfectly. Plus, the imprisoned Mac fed the double false information about his love life, resulting in him ignoring a fiancee he had previously been very loving towards while making advances (which he thought were welcome, but came off as sleazy, thanks to the other woman's lack of interest in him) to another woman. It was then that his friends wised up to what was going on.

By Series:

  • Alex Rider: A recurring theme.
    • The official explanation for Ian Rider's death was that he was speeding, which Alex knows he would never do.
    • When Blunt visits Parker Roscoe, the young man attributes a Hitler quote to his father. Blunt was a friend of Michael Roscoe's and knows he would never quote Hitler, tipping Blunt off to the Evil Plan.
  • On the CW drama All-American, Asher is one of the usual rich kids of the Beverly Hills school who's talked into throwing a huge party at his mansion. The usually laid-back Asher seems intent on making sure there's not a huge mess and no one touches the expensive car. The car ends up being pushed onto the road where it gets damaged. As everyone leaves, inner-city transfer student Spence comes to Asher, who looks as if his world has ended and relates how he knows the reason Asher is so upset. "There ain't no pictures of your family anywhere in this house. You're always forgetting your wallet. And you let everyone else pay for this party. Ain't that hard to spot someone with no money, man." Asher confesses he was rich but his father lost it all in a bad deal and the mansion belongs to some friend they're staying with.
  • In Arrow, Thea's boyfriend takes her to a suburban vacation, Thea falling asleep during the ride. She feels something is off when the skies are so bright and clear and the suburb immaculate. However, she soon realizes that the background sounds end up looping with birds chirping and a dog barking in a perfect sequence over and over. It leads her to discover that the "suburb" is an underground chamber set up by HIVE for survivors of the nuclear war they plan to set off.
  • Batman (1966): When the police chief wipes his forehead with the wrong hand, this tips off Batman that it's actually the villain False Face in a Latex Perfection mask.
  • Blackadder II: Prince Ludwig, master of disguise, tries to sneak into Queen Elizabeth's fancy dress party disguised as Nursie in a cow costume, because Nursie always goes to fancy dress parties as a cow. But he forgot one little thing (or in this case didn't know about it): Nursie is insane and her cow costume looks nothing like a cow. His disguise was too good.
    • An earlier episode had Blackadder and company trying to impersonate a man who they prematurely executed for a last meeting with his wife, and needing to preempt various threads that she fortunately mentions just before meeting him; they almost stumble at the fact that Blackadder pretends to be missing more arm than the man actually lost, but covers it up by claiming to have gotten in a fight with another prisoner. At the end of the episode, he has to do the same thing with the Queen (who happens to be talking about how unexpected it was that the man was a traitor, considering his various debilities...).
    • ''Blackadder Goes Forth". Similarly, Blackadder manages to discover an undercover German agent firstly when George tells him that she had been helping him with the German grammar in a letter to his uncle in Munich, and then later confirms it when she fails to spot that out of Oxford, Cambridge and Hull; one of them is NOT a great university. (As an in-joke, Rowan Atkinson, who plays Blackadder, attended Oxford, whereas Stephen Fry, who plays Melchett, attended Cambridge).
      General Melchett: Quite right, Oxford is a complete dump.
  • On Better Call Saul, Mike is convinced that Henry, a member of a support group, is lying about having a late wife just so he can hang with the group. When friend Anita is dubious, Mike talks of how Henry's tales of meeting wife Judy differ slightly. One story had them sharing their first kiss under the lights of a night game in Wrigley Field in the early '80s. But, as Mike points out, Wrigley Field didn't get lights until 1988. He bets Anita "ten bucks says his next story is different." Sure enough, at the next meeting, Henry tells a story which differs from the one Anita heard before.
  • Happens a lot on The Blacklist as either Liz or Red see something is wrong thanks to a small detail.
    • Red wakes up in Paris hospital, unable to walk with a French inspector telling him he was in a bad accident and that the only way Red is extradited to the U.S. is if he gives up information on Katerina. Red manages to pick the phone of an orderly to find his main screen image has him at a Washington Nationals baseball game. Red then takes a close look at the buildings outside the window and, having been to Paris numerous times, is able to see the skyline is completely wrong for where the hospital is supposed to be. This lets him figure out he's in Annapolis and isn't even paralyzed as this is all a setup to get information out of him.
  • In one episode of Brooklyn Nine-Nine, both Charles and Rosa apply to rent the apartment of an elderly woman who passed away and go to great lengths to butter up the landlord. When he rents to someone else, they start wondering if he has a reason not to rent to cops, because on paper they are very desirable tenants, and find that the woman was poisoned because her apartment was rent-controlled and the landlord wanted to jack up the price.
    • In the Season 5 Episode 99, Jake realizes that Holt has been sabotaging their trip back to New York after a cop mentions that he got a call about a criminal using a "bovine transport unit" to traffick drugs. Jake figures out that it was Holt who called in the tip because anyone else would have just called it a "cattle car." Once Jake figures that out, he comes to the conclusion that every other misfortune that befell them on their trip was also Holt's doing.
    • Holt brings in his old friend, brilliant detective Dillman who prides himself on a Sherlock Scan that accuses Jake of a prank in the station. Jake reveals that Dillman was fired from the San Francisco PD because of his arrogant attitude. Jake relates he figured it out when Dillman talked about using a special database for information as routine...unaware no police force has used that system in five years. Even Holt realizes there's no way a supposedly brilliant cop like Dillman could make such a mistake.
  • Castle's eponymous character is rather good at this, considering his eye for detail thanks to approaching every investigation as a novel plot.
    • Right from the pilot, he recognizes that several crime scenes copied out of his books have details that aren't quite right (the wrong color dress, the wrong species of flower), and since the supposed perpetrator was literally obsessed with him, he would have been incapable of getting the details wrong. Though he then misses the thread (which Beckett easily catches) that the real perpetrator is too ready with an alibi, when he should have had to at least ask for dates.
    • The episode "Once Upon a Crime" has a literal example. A series of murders occur with the women dressed as fairy tale characters and left in public places with the costume bows tied in a certain way. They rescue one woman (Meghan Markle) who was in the same position. However, Beckett and Castle realize the woman's bow was tied in the wrong way and at the wrong angle...as she did it to herself. Which means she's the killer and tried to make herself look like a victim to throw the cops off.
  • Car 54, Where Are You?: In "Here We Go Again", the plot is started off with this. An old criminal discovers from one of the main characters that the only thing they had done wrong on a heist they pulled many years ago and served jail time for was that they had disguised as police wearing winter uniforms instead of summer uniforms. This set off a funny episode as the criminals pull together their now-aged gang to pull off the heist correctly this time. They pull it off, but are all too weak to pick up the gold bars. They then escape the bank wearing the correct summer police uniforms... from the 1920s, not the Present Day (at the time the episode aired) 1960s uniforms.
  • Deception (2018) has a mysterious woman providing illusions to crooks for escapes/thefts/other crimes. Superstar magician Cameron Black is able to see these tricks (a few of which he's used) and helps the FBI in figuring them out.
    • The pilot has Cameron telling the FBI a plane did not actually explode, citing how an explosion in such an enclosed hanger should have caused far more damage and the details of how it was literally driven away.
    • FBI agent Kay Daniels proves she's good at this too. When a banker for a crime cartel shows up to make a deal, she realizes his suit is Brooks Brothers, not the fancy European suits the man wears and figures out it's Cameron in disguise.
    • That mysterious woman (who set up Cameron's twin brother for manslaughter) calls him and Kay to taunt them on "the game is just beginning" and they have no idea where to look for her.
      Cameron: You're in the international terminal at Frankfurt. (woman looks around in shock) I've spent the last year flying around the world, I know every airport has its own acoustics. And Frankfurt pipes in muzak constantly like they're afraid people will forget Beethoven is from Germany. Did you look over your shoulder just now?
    • A bomber puts explosives inside a museum room and demands a ransom or he'd blow it up with a young worker. Cameron manages to rescue her with Kay going over the remains of the paintings in the explosion. A major art fan who's been to this museum several times, Kay realizes that the brush strokes in one of the remains isn't right and has it tested to find out the paintings were fakes and the whole thing was a distraction for a theft.
    • Investigating the death of a radio host who ranted on conspiracies, the team are trying to find clues in his apartment. Cameron surprises them by pulling the guy's microwave off the wall to reveal a hidden safe. He relates the guy had once ranted on microwaves being part of a government plot so owning one himself was odd.
  • On The Defenders (2017), Jessica Jones is going over records for a property going back to the early 19th century. Her attention is caught by how all the deeds and checks and such were signed by a woman. As she compares the signatures, Jessica is rocked to see that, while the names change, the handwriting is identical... meaning it's been the same woman all this time. She then sees that the handwriting matches that of Alexandra and thus, as impossible as it seems, Alexandra has been maintaining this property for two hundred years.
  • The Deuce: Intrepid Reporter Sandra dresses up like a prostitute to write a story about prostitution around the Deuce. After she gets picked up by a paddywagon, patrolman Chris spots that she's an impostor by the fact that her shoes are too expensive.
  • Doctor Who:
    • "The Girl in the Fireplace": After she meets the king for the first time, Reinette notices someone standing in the corner of the room who has been standing still and staying quiet for an unnaturally long time, and demands they show themselves. It turns out to be one of the clockwork droids.
    • "The Beast Below": Elizabeth X says she has been ruling Starship UK for ten years. However, as the Doctor points out, her antique porcelain facemask perfectly fits her face, and hence it stays on all the time. She's actually been ruling for over two hundred years, having her memory periodically erased.
    • Attempted in "Amy's Choice". The TARDIS team are being flipped between two realities, and they need to work out which one is too fantastic to be real — but Rory and Amy point out that this is difficult but when you're in a time machine that's bigger on the inside with a bowtie-wearing alien. Not to mention the fact that both realities are fake — only the Doctor realizes the Dream Lord has already given that fact away.
    • "Asylum of the Daleks": What at first looks like a case of Skewed Priorities is actually this. Oswin Oswald was supposedly able to keep the Asylum's security system from turning her into a Dalek herself, and has been fending off the Daleks in her escape pod and making soufflés for a year. The Doctor realizes that she couldn't have, since soufflés require perishable ingredients like milk, which Oswin would have no access to while trapped in her escape pod. It turns out Oswin did not escape being made a Dalek, but was able to keep her own mind. All the scenes with her in the escape pod? It's her Battle in the Center of the Mind against Dalek conditioning.
    • "The Day of the Doctor": The Doctor(s) forces peace talks (to prevent detonation of a nuclear bomb) between three UNIT members and three shapeshifting aliens copying them by making everyone forget which is the original and which is the duplicate. One of the humans is asthmatic. Her duplicate inherited the asthma, but not the inhaler, causing both to realize who's who. They keep quiet to allow the peace talks to continue, revealing that the Doctor's plan had worked.
      • They continue the ruse later on in order to ensure peace between the humans and the Zygons. When one of them is killed by Missy, the other one is devastated, since they've grown so close they may as well have been sisters (maybe even closer than the human one's real sister). The Doctor (and the fans, of course) keeps trying to guess whether the survivor is human or Zygon, but she's too smart to slip up. Eventually, another Zygon takes on her appearance in order to continue the tradition. This means that either the human-Zygon pair is restored, or there are now two Zygons pretending to be the dead human.
    • "Spyfall": After boarding Barton's plane, the Doctor realizes that there's something fishy about "O", the former MI6 agent she and her companions have been working with, because he said that he's bad at sprinting. But the files on O that the Doctor's read described him as a champion sprinter... he's actually the Master, having murdered the real O on his first day at MI6 and stolen his identity. The Doctor never met the real O.
    • "Orphan 55": When Hyph3n attempts to prevent the Doctor from entering a "linen cupboard", the Doctor stops her by pointing out that the door's lock is far too complicated for it to actually be holding linen (the door actually leads to the security room).
  • On Dynasty (2017), Fallon is suspicious when her long-absent mother Alexis returns and inherits the family estate. Alexis talks of how she's spent the last decade in Europe but Fallon is convinced she has an ulterior motive. Fallon goes to Alexis' chauffeur for information with the man cagy. Fallon suddenly notes that the windows on his car are a bit dirty and, having grown up rich all her life, knows there's no way a professional chauffeur would allow that to happen. She starts to press him on which hotel he picked up Alexis from, naming a few. When he cites the last one, Fallon snaps that hotel doesn't exist in Atlanta and he's just an Uber driver. This leads Fallon to the discovery that Alexis is dead broke and been living in a trailer outside Atlanta.
    • Alexis is sued by a woman who claims her radio show advice pushed the woman into a car accident that broke her shoulder and leg. Alexis and Fallon meet the woman but it escalates into Alexis accidentally kicking her. They're about to leave only for Fallon to take a look at the woman's doormat. They return to point out how the woman tried to defend herself with her "broken" arm in a sling. Also, the mud tracks on her mat match a high-heeled shoe which she shouldn't be able to wear with a boot cast. The woman confesses she was faking her injuries to get money in a settlement.
  • Naturally, Elementary has Sherlock Holmes able to spot the one little detail that undoes the entire mystery.
    • Watson soon joins him in being just as adept finding the minor clues to prove the truth. In fact, thanks to her expertise as a surgeon, Watson can often spot a medical condition clue before Holmes does. Also, as Sherlock isn't as up to date with American sports or pop culture, Watson can see something he missed on a case (for example, how a supposed gambling operation is really a front for smuggling as they're making bets on a "Boston vs Milwaukee game" when no teams of that city play each other in three months).
    • A rare case of neither of them spotting it when they investigate the murder of a doctor who was a "Doomsday prepper" and invested several thousand dollars in a supposed high-priced bunker. Investigating it, Holmes and Watson quickly find out it's a scam to rob rich people. They meet a man who turns out to be a reporter about to expose the scam himself. He reveals he'd been doing a story on it and soon realized something was up as there was absolutely no paper trail for the hundreds of gallons of fuel and numerous supplies such a place would require.
  • The Enemy Within uses this a few times.
    • When Erika warns Keaton that new team member Anna is a mole for terrorist mastermind Tal, Keaton is wary. However (as he tells his team), he's convinced when he goes to Anna's apartment, which she claims to have lived in for two years and sees barely any personal items around.
    • Anna figures out Keaton is onto her as he notes how he tends to clench his fists whenever telling a lie or hearing her tell one.
    • On a trip to the CIA, Erika's expert eye is able to tell how certain agents who only work on matters of South America are in the office with U.S. agents and realizes they're sharing intel on Tal up to something in Cuba.
  • Happens in an episode of Family Matters. When a criminal's brother attempts to kill Steve, he disguises himself as Carl's partner hoping to gain access to the hotel room he and Steve are hiding out in. Carl says "see you later", the man says "okay"...and Carl immediately knows what's going on because his partner would have said "not if I see you first".
  • On Famous In Love, Nina Devon tells son Rainer that his father was a stuntman she had a fling with and died before he was born. In reality, Rainer is the product of an affair Nina had with producer turned studio chief Alan Mills who is also unaware of the truth. On a trip to China, Alan is surprised to find Rainer suffers from the same motion sickness he gets and had once had a drinking habit. When Rainer wants to do a stunt, Alan says he's only 20 but Rainer says he's really 23 and Nina just "aged me down" for his acting career. He mentions his father meeting his mom on a movie, Alan not remembering his "dad" but clearly how he and Nina were involved at the time. It pushes him to get a DNA test and confront Nina.
    • Later in the series, Rainer talks to a stuntman who knew his "dad" and reveals the man was actually gay. This leads Rainer to make the same conclusions as Alan to figure out the truth.
  • Averted on Fringe when Olivia and her alternate universe versions exchange places. Their friends and colleagues begin to suspect something is amiss but don't figure it out on their own before other factors reveal the ruse.
    • Olivia has been given most of the memories of her alternate and made to think that she was the alternate. Her slip-ups in the façade actually save her live at one point as following correct procedure would have gotten her killed. Others attribute her strange behavior to the injuries she supposedly received in an explosion. Her last slip-up is telling a girl that she is FBI in the middle of a gunfight as she rescues her. No attention is drawn to it until the girl asks at the end what the FBI is, in front of her boss who tells her that it hasn't existed in their world for years.
    • The alternate Olivia actually has to fake things based only on files and a very thorough briefing. She masks her slip ups as "trying new things". Peter starts getting suspicious, but is distracted by them becoming a couple. Liv is a wee bit miffed when she gets back.
  • In the pilot episode of Good Girls, Annie's cover is blown during the robbery because the manager/her boss recognizes her distinctive lower back tattoo, which she could have covered up with a longer shirt. He's not at all a nice person, and this leads to complications.
  • The Good Place. In the first season finale, Eleanor figures out that she's actually in the Bad Place upon realizing that all the aggravation she and the other humans caused each other was a deliberate attempt to make them all torture each other. When Michael wipes the humans memories, reboots the neighborhood, and modifies it to keep the humans from figuring out the truth, Eleanor pull this off again. He tries again literally hundreds of more times, but fails every single time. During one reboot, some relatively minor details manage to tip off Jason, who is as dumb as a brick.
  • In Harper's Island, Abby realizes the identity of the murderer, Henry Dunn, when he claims not to have seen his friend Sully, when Abby knows that the coast guard spoke to both men at the same time. It's a bit late by then.
  • Hawaii Five-0: In "Wehe 'ana", Danny is protecting a coma patient who's suddenly become the target of criminals. When a nurse comes in to "check on Mr. Makino" — who the rest of the staff only knew as "John Doe" — Danny knows she's a hitwoman.
    • Steve and Danny help their old former MI-6 ally Langford in keeping an eye on a flighty British heiress whose mother is an old friend of Langford's. When the girl goes missing, the trio go after him with Langford very intense threatening people to find the girl. They rescue her from a white slavery ring to return her to her grateful Duke and Duchess parents. As they walk off, Danny dryly asks if the girl knows Langford is her real father. While Steve is shocked by that, Danny (a father himself) brings up Langford's behavior and knows that only a dad would go to such lengths. He also brings up how the girl has exactly the same sneaky style Langford did and Langford didn't look happy about the girl hugging her "father." Langford admits it's true but prefers the girl not know.
  • In an episode of Hogan's Heroes, the POWs suspected that a German spy has been placed among them. The suspect, who passed the usual questions about American society and such, told them that he didn't speak any German. They staged a fake fire while the man is sleeping, and as the suspect is waking to the confusion, Kinch, who spoke fluent German, told him to go out of the window, which was located across the room. When the suspect immediately went there and started to try to get out, the men knew he was a spy.
    • Another episode had a spy inserted by Major Hochstetter that averted most of the blunders that other infiltrators in the series usually commit: he knew the correct codephrase, didn't fall for any bluffs, was up to date on minute details of Americana, had an impeccable cover story and had trained himself not to respond to German. The ruse is only exposed when, during a visit by Hochstetter to Stalag 13, Hogan sees one of the Major's SS goons snap to attention as the spy passes by, as they are trained to do for SS officers but would never have done for a POW, regardless of rank.
  • In Hyakujuu Sentai Gaoranger, the team is confronted by another Sae/GaoWhite after they retrieve an egg, the only difference being that one Sae was wearing her Belle Tiger jacket and the other wasn't. The two girls tussle and Sae loses her G-Phone, which Kakeru/GaoRed grabs. and both Saes attempt to get the device back. The rest of the team and Tetomu are confused and uncertain who's who. However, Kakeru spots some flowers on the ground and decides to pick the jacketed Sae. She steps on them and Kakeru calls her out as the fake, but they discover the other one had also stepped on a flower! However, when the other quickly panics and goes to fix it up, the jacketed one reveals her true colors.
  • Played straight and then subverted in an episode of Kenny vs. Spenny. In the "Who Can Be Obese Longer?" competition Kenny uses extensive prosthetic makeup to make himself look like a fat person. What this lets him do is remove the extra weight they're forced to wear without Spenny noticing. After a while Kenny comes home and Spenny notices something: Kenny lost the top of his index finger as a child, yet Kenny in the fat suit has it. Spenny concludes that Kenny is faking and uses some spy equipment to see that Kenny is in his room playing video games without his weights on. Spenny confronts "Kenny" and takes off his weight. Then the subversion kicks in: Kenny had a prosthetic finger applied when he was getting the fat makeup put on because he knew Spenny would notice it. Kenny revealed himself to be the real deal and to still be wearing the weights (he put them back on) and won the competition. The "Kenny" in his room was someone made up to look like him.
  • On Killjoys, Zeph may be rather quirky but does have a knack for this.
    • Zeph is among other RAC recruits taking part in a mission where a deadly toxin starts affecting everyone. She manages to blow out an airlock as she's figured out this was all part of a simulation. She explains that the toxin seemed to affect everyone equally when the varying body chemistries and sizes should have made differences. She also noted the lack of sweat on D'avin and how he didn't seem too concerned when Dutch was facing death.
    • In season 5, everyone has had their memories wiped and put in new lives. Despite this, Zeph is able to sense something is wrong as this supposedly semi-arid moon rains exactly twice a day like clockwork. This leads her to figure out the entire place is an artificial world whose environment is collapsing.
  • Law & Order occasionally has the lawyers look at the defense counsel's witness list, and realize that expected witnesses are missing. Upon talking to said not-witnesses, they usually find something that would've sunk the defense's case. And it does. The detectives occasionally pick up on stuff like this too.
    • An episode of SVU had the detectives realizing that their murder victim was in fact alive and masquerading as her own twin after running her dental records; the teeth on the body are structurally identical to the victim, but the victim had some dental work that wasn't showing up. Her husband never suspected, but when questioned by the detectives, realizes that three years prior (when the victim presumably disappeared) that his "wife" suddenly stopped going to church whereas she had previously gone every day and claimed to have misplaced her crucifix, which had in fact been buried with the victim.
    • In one episode of SVU, two girls who helped their Alpha Bitch clique leader murder their friend are trying to claim they only went along because they were afraid of her. The argument is convincing and Novak is worried the jury might buy it, until one of the girls makes a comment on the stand about being chosen to lure the victim out of her house because it was her birthday. Novak then realizes the girl just said her birthday was the victim's date of death, in January, but she's wearing a class ring with a sapphire, the birthstone for September. What's more, the victim had had a September birthday, and also had a sapphire class ring that was never found. Novak absolutely hammers the girl on it until the two defendants start turning on each other to protect themselves. Both are found guilty.
    • Another episode of SVU is about a music teacher who happens to have a popular kids show, where he discovers who is talanted enough to compete for a music deal. It establishes that he is a gay man, and is accused of molesting little boys when one in his class comes forward, along with his friend, and both claiming his favorite molesting spot is the boy's bathroom at school or his music room. Soon, many other boys come forward and it looks like a big scandal is happening. The teacher is fired from both his jobs, some of his family disowns him and he is charged for multiple underage rapes. However, Detective Rollins has doubts from the beginning based on a gut feeling. Sure enough, when she is able to talk to the boy alone in the bathroom at his house, she discovers that the same description he used for the school bathroom is the same one at his house. Rollins gets Benson who was interviewing his older sister, and the two soon discover that the boy was lying all along and his older sister and her friend put him up to it as part of a revenge scheme, because the music teacher rejected them years ago from the competition. The charges against the music teacher are cleared, but his reputation is still ruined, and the prosecutor refuses to charge the girls responsible with committing any crimes.
  • Legend of the Seeker: Richard realizes something is wrong when Darken Rahl, in the guise of his former flame Anna, says something she would not have known in "Home".
  • Leverage: In "The Second David Job", Eliot poses as an antiques expert and takes Nate's ex-wife out for coffee while the rest of the gang watch from inside a van. His ex-wife appears to buy it until she looks at one of Eliot's buttons and points out that she bought that exact camera for Nate on his birthday. Cut to her walking up to Nate's van and demanding an explanation.
    • She screwed with Nate's head a little bit first. Justifiably.
    • In another episode, Nate figures out that his long-time rival Sterling is the real father of a girl when he keeps insisting on correcting anyone who calls her stepfather her "father". In addition, the girl is a master chess player and claims her dad taught her, except her stepfather is awful at chess.
  • On M*A*S*H, one of B.J.'s pranks involves setting Winchester and Margaret at each other's throats, offering "helpful" advice to both sides. But he makes the mistake of using the same bit of overly-flowery language with both of them, and then Margaret repeats it while battling with Winchester.
  • Attempted in Mighty Morphin' Power Rangers Season 2 episode "The Wannabe Ranger"; Primator, a monster able to perfectly disguise himself as any of the Rangers in- or out-of-uniform, copies the Yellow Ranger Trini while the eam are performing their individual Super Sentai Stances. Red Ranger Jason says that if they both attack him, he'll be able to Spot the Impostor by the way they fight; subverted in that the real Trini declines to do so out of friendship, while Primator-as-Trini just jumps at him.
  • Occurs occasionally in Mission: Impossible, as the plans often involve some sort of deception. Of course, it often turns out that the team left loose threads to be spotted on purpose, to trick their opponents into thinking that they know what's going on. The episode "The Mind of Stefan Miklos" has the whole point of their plan be that Miklos spots the threads and draws a conclusion based on it. The hilarious part is the conclusion Miklos draws is the conclusion they want; their bug transmits Miklos admiring the brilliance of the man who came up with the scheme -and pitying him for failing.
  • In the Monk episode "Mr. Monk and the Bully" it turns out the murder suspect was framed by his wife's identical twin sister, who was impersonating her. Monk was tipped off by the fact that the wife and her impostor pronunced "aunt" differently, as they were raised in different regions.
  • The Mysteries Of Laura has the team investigating the murder of a fertility doctor. Laura and her ex-husband Jake go undercover as a couple where the doctor shows an ultrasound of Laura pregnant. As the two aren't together (and Laura hasn't been with a man in months), they know it's a fake and figure the clinic is scamming women by making them think they're pregnant, charging them for expensive treatments, then a drug that replicates a miscarriage. Eventually, Laura finds the killer to have been a husband whose wife had undergone several of these fake "pregnancies". He reveals he figured it out as he's a film editor and on the third go-around, realized the "ultrasound" was the exact same footage as the previous two times.
  • Nicky, Ricky, Dicky, and Dawn In "The Quadfather", Nicky realizes his father is actually the title character (a beaver dressed in a suit) after hearing him sneeze.
  • A guest character on NUMB3RS who had been involved in a crime is being used as part of a sting operation to catch the drug dealer who masterminded the operation. When the dealer's guard reacts violently to him reaching for a flash drive in his pocket, the very nervous informant incredulously asks if the dealer thinks he'd try to pull anything given what happened to his partner, who was murdered by the dealer. Unfortunately, the partner's death wasn't public knowledge, so the drug dealer quickly realizes the only place he could have gotten that information was by having talked to law enforcement. Luckily, the FBI is on hand to prevent the informant from being killed.
  • Red Dwarf: TWO examples in the season 6 opener "Psirens"; the first being when a psiren masquerading as Kryten refers to Lister as "Dave" instead of "Mr. Lister", and the second when a psiren masquerading as Lister gives himself away by playing the guitar as well as Lister thinks he does.
  • On the sci-fi series Salvation, Darius finds his professor, Harris, missing with his home trashed and the man's glasses (a one-of-a-kind pair from his grandfather) left behind. Later, Harris returns, revealing he was on the run from some mysterious foe. He and Darius are joined in a scientific effort to stop a deadly asteroid from hitting Earth. Taken by some agents, Darius realizes he recognizes the driver as a man chasing him outside of Harris' home. It then hits Darius that Harris is wearing the exact same glasses from his home. And the only way he could go back to his house when he was supposedly hunted is if he was working with the "attackers" all along.
  • The Rookie:
    • The pilot episode has cops John and Talia investigating a lead at a gym. The owner claims nothing is going on and they can search the place. A former construction worker, John notes that in the hundreds of houses he's been in and helped build, he's never seen anyone put a circuit breaker next to a water pipe. He opens the "breaker" up to show a hidden cache of drugs and money.
    • Later in the series, when Nolan spots a piece of tape over a doorbell camera while working with Detective Nick Armstrong, Armstrong notes that 75% of detectives would have missed that, encouraging Nolan’s own ambition to make detective.
  • A season one episode of Sanctuary involved an abnormal that uses mind manipulation to impersonate people before killing them. It impersonates Will and almost kills Magnus, until Magnus asks for coffee, having previously told the real Will that she hated the beverage, and the fake Will simply says "sure".
  • In Seventeen Moments of Spring, Stirlitz and his radio operator Kathe are Russian Deep Cover Agents inside Nazi Germany. Kathe is nine months pregnant. Stirlitz is worried that she'll start screaming out in Russian when she's in labor. Sure enough, she does. The German nurses call the Gestapo.
  • On She Spies, Jack returns from vacation to give the girls an assignment which is a trap. They see Jack bouncing between his usual bumbling nervous self and a smooth womanizer trying to kill them. D.D. realizes what's going on when she sees a photo from Jack's "vacation" where he was on a resort on the east side of Puerto Rico. Problem being, the background shows the sun setting over the ocean, which is the west. Thus, the "vacation" was all in Jack's mind as he was brainwashed with an alternate identity of a killer.
  • Subverted in an episode of Stargate SG-1 where the team finds themselves in a Cold War-era military base and are mistaken for spies. When an interrogator asks in Russian if they're spies, Daniel, the (American) linguist, replies "Nyet"...
  • Star Trek
    • Star Trek: The Next Generation:
      • Played straight in "Datalore", when Lore tries to pass himself off as Data and slips up by mentioning his "off switch". Data had previously sworn Dr. Crusher to secrecy over it. Other smaller things, such as his use of contractions (whereas Data does not) tipped them off to the charade.
      • "Future Imperfect" has a double example. First, Riker is in a simulation designed to make him think that it's 16 years in the future, and he's a widowed single father serving as the new Captain of the Enterprise. Things seem off, but he isn't able to prove that it's a simulation until he sees a picture of his dead "wife" Min Riker. Turns out that "Min" is actually "Minuet", an artificially created woman from a holodeck simulation; the aliens scanned his mind for memories of a woman that he loved, but didn't bother to verify whether she was a real person.

        After that, the deception is "revealed" to be a Romulan simulation. But then a young boy imprisoned by the Romulans (who previously appeared as Riker's "son" Jean-Luc) refers to one of his Romulan captors as an "Ambassador"; he's actually a commander, and only appeared as an ambassador in the simulation—which the boy couldn't possibly have known. It turns out that the Romulan prison is also a simulation, and the boy was responsible for the simulations all along; he's a lonely orphaned alien who wanted to convince Riker to spend time with him. In the end, Riker takes him back to the Enterprise so he doesn't have to be alone anymore.
      • In "Ship in a Bottle", a Holodeck Malfunction that causes handedness to flip serves as the crucial clue to figuring out what Moriarty is up to.
      • In "Inheritance", when Data meets his "mother", Dr. Julianna Tainer, the scientist who co-built him, he is pleased. When a cave-in occurs, Julianna is revealed to actually be an android (the real Julianna died years before and her husband uploaded her brain patterns into an android without her knowledge), which Data knew. He tells Riker his attention was caught by Julianna doing complicated math equations on the spot. He then saw that her blinking was the same pattern as Data's own, a formula that made their blinking seem random. The final piece was Data hearing Julianna rehearse for a musical performance then replicate the piece in perfect note and pitch, which was humanly impossible.
    • Star Trek: Deep Space Nine
      • Subverts in the episode "Armageddon Game". Keiko O'Brien becomes suspicious of the recording provided of her husband Miles' death, as the time stamp shows it's late in the day and computer analysis shows that the cup he's drinking from (shortly before an explosion) contains coffee, and she knows her husband never drinks coffee in the afternoon as it keeps him awake at night. Sure enough, the video has been faked, and her husband is rescued. He finally makes it back home, and soon after orders a cup of coffee...in the afternoon. She was Right for the Wrong Reasons all along.
      • The episode "Inquisition" had Bashir in a series of events that made it look like he was unknowingly betraying the Federation to the Dominion. Just when it looked like all his friends were convinced that the accusations were true, O'Brien swiftly moves his arm out of Bashir's grasp and Bashir knows that he dislocated his shoulder the previous morning. That made him realize that everything around him was just a holodeck simulation.
      • In "Duet", the first clue for Major Kira that the Cardassian war criminal Gul Darhe'el is not who he says he is comes when he mentions the name of Kira's former resistance cell. Kira doesn't think anything of it at first, but Odo finds it incredibly suspicious that Darhe'el, whose duties did not involve fighting the resistance, would know (let alone remember) such a specific piece of trivia. He claims to have seen her name in reports he read in his spare time, which Kira probably would have bought, but the brief doubt had driven them to seek out other evidence that further unraveled the man's story (most notably, Gul Darhe'el had never contracted the rare disease that had drawn Kira's attention to this traveler in the first place). It turns out he's actually Aamin Marritza, a file clerk who worked under Darhe'el, posing as him in an attempt to appease his own conscience and have his people admit what they did to the Bajorans.
    • Star Trek: Picard: In "The Impossible Box", Hugh is quick to note that Picard would not suddenly come to the Artifact after all these years for whatever official purpose he claimed, then promises to help however he can.
  • Stranger Things: Hopper immediately realizes the people at the lab are hiding something when they show him exterior shots of the lab from the night after Will disappeared, because the video shows a calm night, but it was torrentially raining.
  • Obviously, Veronica Mars has the teenage detective spotting clues to figure things out. She often relates how she was onto something early on, just needed to prove her theory correct.
    • In one episode, trying to figure out who stole money from a poker game of rich kids, Veronica stops by one suspect, finding his dad answering the door. When she relates how the kid stole the money, the others are baffled as he lives in the biggest house in town and dropped off by limo at school every day. Veronica says she found it odd the dad was home in the middle of the day in a huge mansion but then figured out that it's because he wasn't the rich guy, he was the butler/driver and the kid has been playing up being rich this whole time.
    • In the season 2 finale, Jackie, shown to be the rich daughter of a baseball star, tells boyfriend Wallace she's going to attend school in Paris. When we see Jackie later, she's working at her mom's diner in Brooklyn as it turns out that she was just the product of a one-night stand and her father only recently acknowledged she was even alive. She's surprised when Veronica calls her there, knowing all along that Jackie was raised by her hard-working single mom. Veronica states she figured it out when Jackie did a stint at the Java Hutt as she took to waitressing far too easily for an East Side debutante who'd never had a job before. Veronica also knew Jackie's GPA was nowhere near high enough to attend a preppy Paris school and she needs to stop Wallace before he flies to France looking for her.
  • The Walking Dead: Daryl figures out that it isn't really his brother Merle talking to him because he still has both his hands.
  • On Warehouse 13, in Season 1's "Duped", Pete says that Alice's impersonation of Myka failed when she kissed him. The real Myka would never have done so. However, that was a lie to ensure that she didn't find out that the rest of the Warehouse staff had figured it out. The real instance of this trope was when Leena used the Farnsworth to call the fake Myka and ask about her pet ferret. Alice gives herself away when she says that she hadn't named it, which Artie and Leena both knew to be false.

    Podcasts 
  • In episode 11 of Sequinox, it seems like the girls have gotten back to their world. Then Yuki notices that instead of the clothing they had that morning, their outfits are colour-coded. Then it turns out that this isn't their world, it's a Power Rangers-themed world.
    • Again in episode 14, right down to them thinking they're back. Then they notice Caiden wearing glasses. It's a superhero world, and Caiden is Clark Kenting.

    Tabletop Games 
  • The Demoreans of Timemaster are prone to being caught this way. Their obsession with "Perfection" means that when they capture someone and take his place, they don't include any scars or "deformations" (such as a missing fingertip) that the original may have had.

    Theatre 
  • In The Pajama Party Murders, Lola's disguise as Myrtle is revealed when someone points out that, after being called Uncle Cosmo's non-swearing, non-drinking missionary, she swore and took a swig of beer. From there, Pettibone runs down a list of clues that she was an impostor.
  • Mary from The Children's Hour has convinced her grandmother that her two teachers are having a lesbian affair. Her grandmother is an influential person and within days all the students have been taken away by their parents. When Karen and Martha confront Mary's grandmother about her Malicious Slander they ask Mary to explain. Mary keeps to her lie however she says she saw the two doing things when she looked through the keyhole to Martha's door. The problem is, as Martha angrily points out, her door doesn't have a keyhole. Mary then switches her lie to having heard noises from Karen's room, however Karen's room is too far for anyone to have heard anything. When she can't figure out a new excuse Mary says she heard the rumor from a classmate, who heard it when the door was open. Mary blackmails Rosalie to get her to agree with the lie. Karen and Martha spot the thread, however everyone else believes the kids including Karen's fiance.
  • In the beginning of Act 2 of Les Misérables, Javert disguises himself as a disgruntled ex-soldier who helps out the revolutionaries by acting as a spy and attempting to feed them false information. He's only found out when Gavroche reveals him as a cop. It's a wonder they didn't realize this earlier, as Eponine's panicked warning in The Robbery indicates that he's a quite well-known police officer, and he had interacted with three of the revolutionaries (Marius, Gavroche, and Eponine herself) before going undercover.
  • National Theatre's 2014 production of Treasure Island:
    • After Jim overhears the pirates plotting mutiny and reports it to Captain Smollett, Smollett nearly manages to maneuver the would-be mutineers into going ashore where they can be threatened with marooning, pretending that he's unaware of their treachery and offering them the first chance to set foot on dry land after the long voyage. Jim accidentally blows the gaff by making a comment about Long John Silver having been on the island before; Silver recalls that he's been careful never to mention that fact except to his fellow mutineers, realizing that this means Jim heard their conversation.
    • Near the end, Trelawney tries to bluff the pirates by pretending to be the ghostly voice of the late Captain Flint. Armed with details about them supplied by Ben Gunn, he nearly pulls it off until Silver gets suspicious because "Flint" also knows the name of a mutineer who threw in with the pirates on this voyage and was never part of Flint's crew.

    Video Games 
  • Persona 5
    • Madarame tries to tell his student Yusuke that the original painting of his masterpiece, the Sayuri, was stolen, so Madarame had to resort to reproducing fakes. Ann Takamaki points out that his explanation doesn't make sense; how could he have made copies if he didn't have the original? When Madarame digs himself deeper by saying he found a high-quality photograph of it, Ann shoots that down too by pointing out that Madarame's clients are some of the finest eyes in the art world; they'd know if Madarame was trying to sell them a copy of a copy.
    • Spotting a lie is integral to deducing the identity of the traitor to the Phantom Thieves. Akechi's story about being pulled into the Metaverse and awakening his Persona seems pretty cut-and-dry, since it's basically what happened to the rest of the Phantom Thieves. But during his first meeting with the Thieves roughly four months prior, Akechi had unknowingly commented on a remark made by Morgana — which couldn't have been possible at the time if it was true, as only people who have been to the Metaverse can understand Morgana in the real world. Once Joker and Morgana realize this, it doesn't take long for them to work out that if Akechi has had access to the Metaverse since that time, then he can only be the "Black Mask" who's been causing mental shutdowns across Japan for The Conspiracy.
    • A far more minor one that the player cannot call out on In-Universe: The player character's guardian, Sojiro Sakura, claims during the earliest parts of the game that he took him in for his probation because he's being paid to do it, framing it as another way to serve as a disciplinarian to the protagonist and keep him at arms' length. If you watch the game show that airs on LeBlanc's TV on 6/2, the answer for that day states that probation officers don't get paid. This is an early tidbit noting the player that Sojiro cares for the protagonist far more than he lets on.
  • Catherine: Vincent gets told by his friends that none of them ever saw Catherine, the woman he supposedly was cheating on Katherine with. As he's trying to find proof that she was real, and not just a figment of his imagination, he recalls that Boss actually talked to her on the first night Vincent met her. Vincent asks Boss about Catherine, who describes the woman perfectly. He ends up running his mouth and revealing himself to be Dumuzid, the man who is behind the nightmares that have plagued men, and who purposefully sent Catherine, a succubus, onto Vincent.
  • Metal Gear Solid: One of the signs that the DARPA chief was Decoy Octopus were that he referred to the terrorist act as the "revolution". No one picked up on it. Despite knowing there was a master of disguise among the enemy, it didn't occur to anyone on Snake's side that he might be impersonating someone.
    • Metal Gear Solid 2: Sons of Liberty featured Iroquois Pliskin, a Navy SEAL. There are a few clues that he's not quite who he says he is:
      He claims to have arrived on the Big Shell via fast rope onto Strut E with the rest of the SEALs but as he says this, one of the sea lice from the undersea dock in Strut A - the way Raiden got in - crawls away from his leg.
      He gives inspiring mottos in the conversation after he and Raiden locate Stillman but, rather than giving the SEALs' motto, he utters those of the British Special Air Service and US Marine Corps.
    • There's another one in the fourth game. The ending of Act 3: "Big Boss's Corpse" is missing the left eye. Big Boss lost his RIGHT eye. Solidus lost his left eye.
  • In Warnings at Waverly Academy, Nancy Drew has the chance to notice that one of the students is actually twins, who take turn attending classes because only one of them was awarded a scholarship. The Spottable Thread is that one twin's bangs are always falling into her eyes.
  • In Eat Lead: The Return of Matt Hazard, at one point an impostor QA shows up, and they each accuse the other of being the impostor, but Matt already knows the red one is bad. How? Well, aside from Good Colors, Evil Colors, she actually flirted with Matt, and gave nothing but bad advice.
  • Quite often in the Ace Attorney series. The defense attorney you're playing as needs to spot a contradiction in a witness testimony, present a theory, and back it up with evidence. Inevitably, this results in some Courtroom Antics to help catch the real criminal.
    • During case 4 of the first Ace Attorney game, Phoenix Wright completely bluffs about how someone who had been shot could have carried a bullet from the scene of a crime... and, following it to its logical conclusion, helps prove it.
    • Ace Attorney Investigations 2 has a prisoner impersonating a security guard, only to get uncovered when his pet polar bear goes to him.
  • Professor Layton and company catch the villainous Don Paolo multiple times throughout the series by way of this. His mistakes range from "Inspector Chelmey" flipping out over sweets; when the actual inspector is quite fond of his wife Amile's (who is not "Amy") sweet potato fritters, to "Flora" describing a picture 'she' couldn't have seen, to "Future Dean Delmona" having gray hair in the future despite secretly telling Layton that he wears a hairpiece.
  • In The Force Unleashed 2, Starkiller realizes that a droid is impersonating Juno Eclipse because the real Juno had been shot in the shoulder earlier.
  • Set up and subsequently subverted in Assassin's Creed: Brotherhood when Ezio has Bartolomeo pretend to surrender to his own men who are disguised as French troops. A guard at the main gate asks their business in French and Ezio is able to hold a conversation in it. The guard then asks where in France he's from, Ezio is able to provide an acceptable answer. Apparently, his womanizing days paid major dividends almost a quarter-century later.
    • Every game of (Advanced) Wanted requires this. The newbies who run on rooftops openly aren't even trying, but to spot more skilled players demands that you know what NPCs will and will not do. Then again that might not save you...
  • Metal Slug 3 pulls this off nicely when you first meet Morden, It actually isn't him; his eye patch is on the wrong eye.
  • In Chrono Cross, Kid doesn't realize that Lynx has pulled a Grand Theft Me and swapped bodies with Serge until Serge pulls Kid's knife, intending to kill Lynx while saying "I'll avenge Lucca for you." Up to this point, Kid hadn't even mentioned Lucca to anyone, and calls Serge out on how he could have possibly known anything about Lucca. Kid can't really do anything about it, as before she realizes what really happened, she gets stabbed in the stomach for her troubles.
  • During the fight with Vlitra's Core in Asura's Wrath, the cutscenes before and after the fight show What look like Golden threads woven by The Golden Spider to hold Vlitra inside the planet itself and holds up it's stage.
  • Learning behaviors of disguised enemy Spies is a crucial skill required to successfully combat them in Team Fortress 2. The fact that Spies can only mimic the appearance of a different class means that various aberrant behaviors by "teammates" may mean that they're really not. Things like not shooting their guns, Medics not healing or having their Medi Guns equipped, Scouts not running fast enough or double jumping, seemingly wanting to always be behind teammates, colliding with a "teammate" (you can normally walk right through them)... The Team Fortress Wiki has a list of threads to be aware of and look out for (as well as other Spy counter-strategies) to avoid a knife in your or your teammates' backs.
    • Inverted in the in-game comic "Shadow Boxers", where Miss Pauling is able to tell the Soldier isn't being delusional when he claims that he successfully infiltrated the robot base when he mentions that Gray Mann was raised by eagles, a fact known only to her and the Administrator.
  • In God of War: Ascension, Kratos sees through Tisiphone's illusion because she was wearing the ring of his wife Lysandra.
  • The multiplayer espionage game SpyParty is all about this. The person playing the Spy has to act as closely to the guests as possible while completing their objectives, lest the person playing the Sniper realize they are the spy and shoot them. If you're playing against a really good Sniper, even something as small as looking at a statue and putting it down before the animation is about to loop can blow your cover.
  • Zorua and Zoroark from Pokémon have the ability Illusion, which causes them to disguise themselves as a different Pokemon in their party until they take damage. Well-studied opponents may notice this if they spot a Pokemon using moves it normally can't learn - more everyday opponents may spot the thread if their opponent doesn't interact with the Elemental Rock–Paper–Scissors system in the way it should. It doesn't help that Zoroark has a Secret Art attack that serves as an immediate giveaway.
  • Danganronpa: Trigger Happy Havoc: During the second scene of the game, the main character will note that Junko Enoshima looks different from her cover shots on magazines. This is then played off as the result of touch-ups and editing. Some of her dialogue during Free Time events also seems incongruous with her Ultimate Fashionista title. Chapter 6 reveals that the girl everyone met at the start was not Junko, but rather her fraternal twin sister Mukuro Ikusaba, whose appearance is very similar, but with a few minor differences.
  • One sidequest in Deus Ex: Mankind Divided involves retrieving some data off a 3.5'' floppy disk before some mercenaries hired by Picus can retrieve it, which requires a trip to an antiques store for a (by now 40-years obsolete) disk reader. The store clerk offers to let Jensen rummage around in the basement to look for one, but his overly inquisitive nature, and the fact that he constantly gets the name of his store wrong, tips Jensen off that the "clerk" is really one of the mercenaries, waiting to ambush him.
  • Blackwall casually mentions early on in Dragon Age: Inquisition that he was in Fereldan during the Blight: "Quietly killed my fair share of darkspawn, too." This is the first clue that he's not who he seems, since anyone who's played Dragon Age: Origins will remember that all the Wardens except Alistair and the PC got killed at Ostagar.
  • In Iji, if you kill few enough Tasen in the first few levels, Iji will opt not to call the Komato, who she had learned about from a marooned scout team. Since the Tasen sent a fake "final report" on their behalf, this would result in the whole thing quietly going away in the Komato's eyes... except that the fake report referenced "planetary scan" technology that never worked and only survives as propaganda. So the Komato show up anyway.
  • In Final Fantasy XIV, the player character and Estenien are able to confront and defeat Nidhogg, ripping out his remaining eye. However, they notice something very off - the eye they used to find the dragon and the eye they ripped out are two different kinds. As it turns out, the other eye belongs to Nidhogg's brother, Hraesvelgr, who was guilt-tripped by Nidhogg into passing it over.
  • In Paper Mario, the captured Princess Peach eventually acquires an item called the Sneaky Parasol that lets her disguise herself as one of Bowser's troops. The only person who sees through this is Kammy Koopa, who notices that the 'guard' in question smells strangely nice.
  • League of Legends:
    • Shaco, LeBlanc and Neeko can all create duplicates of themselves to mislead enemies and make them waste abilities on the fake (and, for Shaco, to increase damage output). However, duplicates are controlled by the AI, so they behave slightly differently to humans such as not prioritising Shaco's Backstab passive. More tellingly, all three champions are heavily reliant on abilities, but duplicates can only use basic attacks.
    • Neeko can take an ally's appearance, including their apparent health stats (masking her own health bar). Spotting enemies that aren't trying to escape from unnecessarily-precarious positions can be important to stop yourself taking her bait.
  • Dark Souls:
    • Mimics appear almost exactly like treasure chests, except for some minor differences - more elaborate front designs, slightly open lids, chains that coil in the wrong direction, and so on. Learning to recognise these clues can significantly increase your character's lifespan. (That being said, with the way online connectivity works in Souls games, another valuable tipoff is that if a chest is surrounded by bloodstains and glowing orange messages, it's probably a Mimic.)
    • Some enemies in Dark Souls II appear to be the ghost images of other players up until they attack you. These enemies, however, all have similar equipment (in particular, they all have crossbows), do not fade away like player ghosts usually do, typically have repetitive behaviour, and sometimes do things that players usually wouldn't - for example, in Scholar of the First Sin, there's a ghost near the Shaded Ruins bonfire that is usually found sitting down, a thing players can do but usually wouldn't in the context of an area so full of murderous lion-men and jars that shower you with Curse.
  • In The Legend of Zelda: A Link to the Past, all of the maidens were sealed inside magic crystals. So in the Thieves' Town dungeon, you probably realize immediately that something isn't right when you find the maiden imprisoned in a prison cell. The "maiden" also asks you to take her outside, but if you try to do so, she won't actually let you. Turns out, "she" is actually the dungeon boss in disguise.

    Webcomics 
  • In Cuanta Vida, Jeremy's green eyes and relaxed attitude tip off Jordi that he's dealing with Miguel, the RED spy.
  • Shapeshifting fae Nutmeg from Dan and Mab's Furry Adventures pretends to be her husband, but Mab notices it because she didn't get the mannerism and hoof patterns right. Earlier, Jyrras uses a Magitek patch to pretend to be a cubi, but the disguise is pretty transparent to any real cubi (who are mind readers).
  • In this strip of Girl Genius, despite being in pain from having just swallowed a slaver wasp, Baron Klaus Wulfenbach is able to tell the person he's talking to isn't Agatha Heterodyne from her speech pattern, facial expression and body stance... and he finally recognizes she's (possessed by) Lucrezia from hearing her gloat.
  • In El Goonish Shive, Tom's apology to Susan for missing her on a text messaging service tips Susan off that his intentions are not what they seem to be on the surface. He never asked whether or not she'd been online with that messenger service that night before apologising for "missing" her online... and the messenger service has an "invisible" mode.
  • The Order of the Stick:
    • At one point Elan is replaced by his Evil Twin Nale, despite pretty much every thing he does being a possible invocation of this trope, all his teammates just chalk it up to Elan being, well, Elan. Until that is Nale changes out of the clothes he stole from Elan and takes a shower, at which point Belkar notices that "Elan" smells like Nale.
    • Elan himself realises that the team have been trapped in a Lotus-Eater Machine when Nale doesn't do anything to stop their parents remarrying. This realisation forces him to acknowledge that the remarriage doesn't make sense either, it's just what he'd want to happen.
  • Plane-spotters and birdwatchers do this in this xkcd strip, much to the frustration of a government cabal who need to find something to disguise their surveillance drones as that doesn't have an obsessive spotting community. Turns out, there's a lot of people who like staring at the sky.

    Web Original 
  • At times, This Very Wiki. That "Super Secret Spoiler" wasn't so Super Secret when some extra white space where there shouldn't be popped up.
    • Of course, due to the YMMV finagle, Super Secret Spoiler has been replaced with the normal spoiler.
    • Averted deliberately by some clever tropers by using completely unnecessary spoiler space or adding innocuous information under spoilers in strategic places, and making spoilers longer . . . yes, longer than necessary so their length doesn't give anything away.
  • Parodied in SF Debris's reviews of Star Trek: Voyager, in which it turns out that all the hallucinations and fantasies share one common flaw: Chakotay is too lifelike.
  • Help Not Wanted: Ogrell Syn'Gorrsh speaks in Third-Person Person all the time, but in chapter 6, he tells the four goblin contractors that "I'm not a trustworthy person." They realize immediately that he's been lying about who he says he is, and it's revealed that he's a Serial Killer who pretends to acts stupid so his victims will lower their guard around him.
  • Loves Lost And Found: Maria is having dinner with a strigoi disguised as Hardestadt Delac. While in disguise, the strigoi calls Maria a woman, despite the fact that Maria is non-binary. They notice, and shortly afterwards, Maria kills the impostor.
  • In the Search and Rescue Woods Creepypasta series, the protagonist hears a crying child, and goes to investigate. He then notices something wrong: the "crying" is the same sound over and over again, like a song on repeat. He wisely nopes out of there.

    Western Animation 
  • In the Adventures of Sonic the Hedgehog episode "Tails' New Home", Sonic and Tails meet an elderly fox couple who are apparently Tails' long-lost parents. Sonic allows Tails to stay with the couple, and while reminiscing on their first meeting, remembers that Tails is Only Known By His Nickname, and on top of that, it's a nickname that Sonic gave him. If the couple really were Tails' parents, they would have called him "Miles". Sure enough, the 'parents' are actually some of Robotnik's robots in disguise.
  • Sonic Boom:
    • In the episode "Where Have All The Sonics Gone?", after Eggman and Morpho send Sonic to an alternate dimension, Morpho disguises himself as Sonic to keep up the charade for a little while and attempts to charm and invite Amy to a trip to the canyon. It only takes her a split second to realize what's going on (after giggling like a schoolgirl at the idea of going out with Sonic).
    • In the episode "Vector Detector", Vector the Crocodile is brought in to try to figure out who could have stolen Amy's hammer. When they find the culprit, comedian Wolf Sidekick, Amy is overly thrilled and mentions that her hammer is a one-of-a-kind weapon. This makes Vector realize that a comedian wouldn't want to take a mallet like hers when any old one would do. Thanks to some help from Sonic, Vector finds the real culprit — his manager, who had set the whole thing up for ratings.
  • Beast Wars: Megatron makes a clone of Dinobot that can't transform. Had Dinobot not taken care of the problem, this trope would've resulted.
  • In Code Lyoko episode "Franz Hopper", a Polymorphic Clone impersonates Franz Hopper to lure the heroes into a trap. Jeremie realizes he must be an impostor after the fake Franz mentions the destruction of his video diary (which occurred in a previous episode) — something that the real Franz Hopper couldn't have known about, but that XANA certainly did.
    • "XANA's Kiss" features an inversion where Odd figures out that the Yumi yelling at him is the real her because she calls him a peabrain, something XANA and therefore his clones would never do.
    • In "Distant Memory", after being in a simulation bubble, Aelita notices when her father forgets the name Skidbladnir from a book her father read to her as a child, and then adds later that if he knew anything about her, he would materialize her Missing Mom into it, since she'd give anything to see her again. This helps her deduce that "her father" is really XANA. On the opposite side of the coin, Yumi and Jeremie realize that Aelita is in said simulation bubble because of a chat message from her father, having known the fact that he wouldn't risk it with her, since XANA is actively trying to dump her into the Digital Sea to draw him out.
  • In the Codename: Kids Next Door episode "U.T.O.P.I.A.", Numbuh One crash lands on an island that's a complete kid paradise, which causes him to be suspicious from the start. He finds his team swimming in the island's swimming pool and they all convince him to drop his suspicions and just have fun. Numbuh One was about to, until he remembers, as established in earlier episodes, Numbuh Four can't swim. At that point, it's revealed that he's been trapped in a Lotus-Eater Machine.
  • DCAU:
    • Justice League:
      • In the introductory episode of the Secret Society, Clayface attempts to lure Batman into a trap by impersonating The Flash and calling for "help" against a confederate super-villain. Batman arrives on scene to find that "Flash" appears to have things well in hand:
      "Flash": Looks like I didn't need your help after all, yo. But you can help me tie him up—
      Batman: (throws a batarang at Flash) Catch.
      (batarang hits and electrifies Flash, reverting him to Clayface)
      Batman: The real Flash would have been too fast for that.
      Clayface: ...What gave me away?
      Batman: You overplayed your part, "yo".
      • From the same show, Lex Luthor needs barely a glance at the Justice Lords (currently masquerading as the Justice League) to know that "It's not them." Of course, this might have something to do with all of them wearing completely different costumes. The fact that Superman had just lobotomized someone was also a big clue.
      • In Season 1's "In Blackest Night", Green Lantern is accused of blowing up a planet and killing its entire population. Superman and Martian Manhunter go to check it out and quickly realize that something is off: if the planet really was destroyed, then why has its moon maintained its orbit?
      • In "Legends", after the heroes find their first main clue that something is off about Seaboard City, they start noticing smaller imperfections. The local heroes always work with the same two cops, and the exact same ice cream truck is constantly roaming the city without ever stopping.
    • Batman Beyond: In "Shriek", Bruce Wayne realizes that "his" voice in his head is actually somebody else, since this voice calls him "Bruce", while Bruce refers to himself by a different name in his head. When Terry points out that Bruce isn't Batman anymore, Bruce just says "tell that to my subconscious".
    • Superman: The Animated Series: In "Knight Time", similar to the Billy and Mandy example below, Robin figures out that something is wrong with Bruce Wayne when he smiles on a recorded message.
    • Batman: The Animated Series: The Ninja Kyodai Ken realizes Bruce Wayne is Batman after fighting him in both identities; as Batman tells Alfred, to a trained martial artist, a fighting style is "like a fingerprint".
  • Ed, Edd n Eddy: In "A Twist of Ed", the Ed’s plan to get the Kankers to leave them alone once and for all by using Reverse Psychology, pretending to have fallen in love with them and harass them with unwanted affection the same way they have done to them. Ed and Double D both put on a very convincing performance and have the Kankers trembling in fear at their presence, but Eddy continues to be too scared of the Kankers to even try to flirt with them. When Double D forces Eddy to take a turn to seal the deal, the Kankers notice a nervous sweat drop roll down his face. This immediately tips them off that the Ed’s are only faking their attraction to them, which not only restores their own crushes on the Eds, but has them come up with a plan to trap them and take revenge on them by pretending to still be scared of them.
  • Family Guy: "Wait a minute; your ass just sneezed! And horses can't talk! No, no nothing about this adds up at all."
  • Foster's Home for Imaginary Friends: In the episode "Bloo's Brothers", Mac takes Bloo to Show-And-Tell, where he's such a hit that all the other kids at school decide then and there to imagine up their own Bloo knock-offs. Unfortunately, despite all their creative spins on the concept (the Bloo clones tend to look nothing like Bloo, and most are downright bizarre), they're all Jerkasses at heart just like the original and end up getting dropped off at Foster's, where Bloo wastes no time organizing them into an army to take over the world a 100-part choir. However, when Mac shows up with two tickets to the Ice Charades, the other Bloos scramble to impersonate the real one in the hopes of going to the show. In the end, Bloo is pitted against a nigh-perfect clone as Mac grills them both to try and determine which is the real one: the fake gives himself away by launching into a Glurge-filled friendship speech.
  • In one episode of Gargoyles, Goliath is plagued by hallucinations, this being the work of the vengeful spirits of Hakon and the Captain, which culminates in Goliath being confronted with an illusion of his slaughtered clan members who blame him for their deaths. Goliath is able to see through the facade when Hakon and the Captain make the mistake of introducing an illusion of Goliath's former love Demona, who unbeknownst to them had escaped being massacred, cluing Goliath in that everything he's seen wasn't real.
  • Gravity Falls:
    • "Into the Bunker:" When Dipper asks for a sign to decide which Wendy is the impostor, the shapeshifter gives him a suggestive wink, which Dipper knows the real Wendy would not do as of yet, and the real Wendy gives a legitimate sign, so Dipper correctly strikes the impostor.
    • "Weirdmageddon Part 2: Escape to Reality:" In Mabeland, a frustrated Dipper talks to Wendy, who says that if Dipper were older, she might have wanted to date him. At first, Dipper gets really happy at the thought, until Wendy yet again gives him a wink, a Call-Back to "Into the Bunker," revealing that this Wendy is just a part of the fantasy world.
  • The Grim Adventures of Billy & Mandy: Nergal Jr. tries to impersonate Mandy, but Billy can tell it's off because she was smiling. Weird use of this trope, as Nergal Jr. keeps his distinct glasses even when disguised as others. Billy does notice the glasses, too, but it's the smile he brings up first.
  • Agent Jay in Men in Black once had to find a disguised alien ship. A quick look at the skies over New York, and he singles out a blimp. Elle asks why a blimp over Yankee Stadium was odd - Jay notes there's no game that night.
  • In an episode of A Pup Named Scooby-Doo, after capturing the ghost of Pervis Parker (an Elvis Presley expy), and revealing it to be the owner of the Pervis Parker museum, Velma states she first became suspicious of him after he made a long complaint to the kids about business being terrible, but when Daphne bought tickets to the museum, he was easily able break her large bill.
  • One episode of Regular Show, "Temp Check", features this. Doug, a shapeshifting mole attempting to take over Rigby's identity, is for the most part successful in convincing Mordecai and his coworkers that he's the real Rigby, but Mordecai sees through the facade for two reasons: the real Rigby whining about being "replaced", and the fact that Doug hugged Mordecai just before that (an act established earlier on in the episode that Rigby himself would never do).
  • In the Rugrats episode "The Trial", the babies set up a trial to find out who broke Tommy's clown lamp with Angelica in the role of prosecutor. The babies realize at the end Angelica was the one who broke the lamp when her alibi of taking a nap at the time fell apart because she somehow knew everything the babies were doing. Because of her usual demeanor, Angelica gloats because she knows the babies can't say anything to the adults, but ends up outing herself anyways because she forgot Didi and Betty were in the next room and could hear everything.
  • In The Spectacular Spider-Man, Captain George Stacy is able to identify that someone is impersonating Spider-Man — twice — by observing the differences in build and height compared to the real thing. J. Jonah Jameson stumbles into the realization during the first instance when the real Spider-Man (who's currently wearing a different costume) immediately begins to push his buttons.
  • Spider-Man: The Animated Series:
    • Chameleon duplicates Nick Fury's appearance from his newspaper obituary, but the paper accidentally flipped the photo, putting his eyepatch on the wrong side. Spider-Man notices the difference immediately.
    • Later in the same episode, Chameleon poses as Peter Parker to get into position to kill his target. Spider-Man easily spots him (since Spidey, of course, is Peter Parker) and takes him out. As Chameleon is being taken away, he demands to know what was wrong with his disguise, at which point Spider-Man just makes something up.
  • Star Wars Rebels: In "Through Imperial Eyes", Grand Admiral Thrawn is searching for the identity of a Reverse Mole in the Imperial ranks. After it seems that Lieutenant Lyste has been revealed as the traitor, having helped a rebel prisoner escape, a stormtrooper brings Thrawn the helmet the prisoner was wearing — which has a stylized lothcat painted on it, which Thrawn recognizes as being in the style of Sabine Wren. This leads him to deduce that Agent Kallus is actually the traitor, because the helmet most likely belongs to Ezra Bridger, who Kallus would have recognized, and the fact that he didn't report Ezra's presence . . . well.
  • Steven Universe: In "The Trial", the Defense Zircon spots several inconsistencies with the story of Rose shattering Pink Diamond. At this point, Rose Quartz was an infamous, wanted criminal, and the only one of her gem type that was active at the time. So how did she get past all of Pink Diamond's entourage without somebody recognizing her and at least sounding the alarm? On top of that, the explanation that Rose's sword shattered Pink Diamond makes no sense, because it was made so it couldn't shatter Gems, much less one of the most powerful Gems in the entire universe. The Defense Zircon concludes that Pink Diamond was killed by someone close to her, someone who could get past Pink's entourage with no interference, someone who'd have the authority to have the entire situation covered up, someone... like another Diamond. Of course, right after this, the Defense Zircon realizes what she just said and tries a Verbal Backspace, but the judge for the trial poofs her immediately.
    • Another instance, related to the same event: In "Your Mother and Mine", Garnet tells Steven the Crystal Gems' side of the story in a silhouetted flashback. Flashback!Rose Quartz wields her sword in her right hand, while the real Rose Quartz wielded her sword in her left hand, keeping her right hand for her shield (which Flashback!Rose didn't have).
    • In "A Single Pale Rose", the reason for the inconsistencies is revealed: Rose Quartz and Pink Diamond were one and the same. Her "shattering" was faked, with Pearl shapeshifted into "Rose".
  • In Young Justice, Aqualad and Garth steal the uniforms of two of Black Manta's henchmen and try Dressing as the Enemy to get close. Black Manta sees through it pretty much immediately when he notices that Aqualad tucked his water-bearers into his belt.

    Real Life 
  • There is a story of a British spy in occupied France during WWII who was exposed after ordering "cafe noir" (black coffee). A local would have known that, with milk being scarce, the "noir" was redundant as that was all there was on offer.
  • There are also many, many cases of German spies being picked up almost immediately after arriving in Britain, largely because the various feuding Nazi organisations' information was woefully out of date. In particular, they never seemed to grasp the intricacies of the British rationing system (for example, trying to pay for meals in restaurants with food ration tickets).
  • There were stories of British spies nearly getting caught for putting spoonfuls of soup straight into their mouths (in parts of France at the time it was customary for women to sip from the side of the spoon) and, of course, forgetting that the French drive on the right side of the road. Similar stories include (in this case, US) spies outed when they switch their fork from the left to right hand to eat, rather than the Continental style which keeps the fork in the left hand.
  • There's a true story about a suspected German spy being questioned for several days. The interrogators had their suspicions, but there was nothing definite, so they let the man go. He blurted out, "Danke..." The story is also told the other way around - an American spy, after days of interrogation, being told in German, "Well, seems you're not a spy after all, you can go" to which they replied - in English - "Thank you!"
  • And another one about two German spies entering a bar in USA and making the following exchange with the bartender:
    Spy: Two martinis, please.
    Bartender: Dry? (homophonic to German "drei" - "three")
    Spy: Nein, zwei!
  • And another one about German infiltrators during Battle of the Bulge:
    Spy (at American gas station): Petrol, please!
  • Whenever German spies infiltrated the Soviet army, they usually had perfect and impeccable legends, accents and documents. But the staples on their documents were shiny stainless steel — the USSR was still stuck with iron staples, which rusted.
  • Germans-dressed-as-Americans during the Battle of the Bulge were given away due to their forgers correcting an intentional spelling error on the standard GI identity cards.
  • American spies were supposedly outed by the Germans for crossing their legs the American way, by resting their ankle on the opposite knee. Europeans cross their legs by resting the back of one knee over the other.
  • Many a German spy was outed in World War II for failing to comprehend the mind-numbingly complicated British Imperial monetary system. Until 1971, the complex coinage, nonsensical divisions of currency (240 pennies to a pound, quarters of pennies, etc.), and the numerous slang terms for the various denominations meant that merely counting change was extremely difficult for foreigners. This also nearly tripped up a sympathetic spy, Juan Pujol Garcia, a Spaniard who took it upon himself to feed false information to the Germans (and who was later inducted into the British spy network). Instead of trying to add up the totals on the fake expense accounts from his fake agents in the UK, he simply sent out itemized lists of things (like information) they had supposedly bought.
    • One of Pujol's fake reports claimed that in Glasgow (which Pujol never visited, being based in Lisbon during this time) there were men who "will do anything for a liter of wine". Not only do Scots mostly drink ale or whisky, they use the Imperial system of measurements, not the Metric. Somehow the Nazis never noticed this. (Then again, selling wine in metric measurements is quite common, even in the US.)
  • Legend has it that the "Romeo" spies used by East German spymaster Markus Wolf to prey on lonely West German women who had access to relevant information eventually got compromised by German train conductors who noticed their totally unfashionable haircuts as soon as they entered West Germany.
  • Roger Bushell, the mastermind behind the famous WWII "Great Escape", and his traveling companion were captured in this way. The pair were pretending to be French, but an officer became suspicious and fired off a sudden question in English. Bushell's companion (who was actually from France and spoke French as his first language, but had grown accustomed to speaking English with his fellow POWs in the camp) instinctively responded in English as well. A fictionalized but relatively close version of the incident is depicted in the film version of the story (see entry under "Film").
  • Shibboleths are words that rely heavily on language-specific pronunciation. These have often been used to distinguish infiltrators from native speakers. Of course, they are useless against traitors.
    • The Dutch used the name of the port town Scheveningen to unmask Germans.
    • In 1302, during the Bruges Matins the Flemish used the phrase "Schild en Vriend" ("Shield and friend") to identify and murder French sympathizers.
    • In 1312, soldiers of the Polish duke (later king) Władysław Łokietek rooted out foreign members of a burgher revolt in Kraków by forcing every interrogated citizen to say "soczewica koło miele młyn" - a nonsensical note  string of Polish words, which were difficult to pronounce properly in fast succession by anyone not intimately familiar with the language. The city was summarily punished for the revolt anyway, but the foreigners identified this way received some extra attention.
    • The term itself comes from The Bible, in an account where, during a conflict between the Gileadites and Ephraimites in one of Israel's pre-monarchy civil wars, the Gileadites identified fleeing Ephraimites by their pronunciation of the word shibbólet (שִׁבֹּלֶת) (meaning "ear" in the sense of "ear of corn," i.e. "the part of a cereal plant that contains the grains"), which would have been pronounced sibbolet in the Ephraimite dialect.
  • Another WWII story tells of a soldier who tried very hard to pass as a civilian while in Europe. He got new clothes, new hairstyle, learned the local language, etc. One day, while waiting on the curb with two bags of groceries in his hand, a German walks up and basically greets him with "Hi, Soldier!" The reason? He had two bags of groceries in one hand, because the military ingrains the habit of keeping your other hand free to salute.
  • During WWII, German spies would often try to infiltrate Britain via neutral Spain, posing as Swiss businessmen in order to travel to Spain. The problem was, German standards of discipline were too high. German spies were under standing orders to stay sober, not frequent brothels, and absolutely not to deal on the black market, whereas given how expensive and heavily taxed cigarettes, saccharine and other luxuries had become in Switzerland during World War Two, MI6 could tell with a good degree of accuracy who were real Swiss businessmen and who were spies simply by offering to sell them some cigarettes or nylons on the sly. At one point, the German intelligence services were receiving hundreds of reports from agents “in London” per month, all coming from agents caught and turned in Spain, writing fake reports from Barcelona using "The A-Z of London" and copies of The Times to keep their fake reports realistic. All because the spies were more honest in their dealings than the civilians.
  • More hapless German and Russian spies in and after WWII ran into trouble when, if they made it to England, they ordered tea without milk whilst posing as working-class Brits. That would be seen as a little odd today. In the '40s and '50s, you may as well have turned up with a sandwich board saying “I’m a spy”.
  • An interview with early female CIA operatives suggested that women at the CIA were better at this than men. One now senior analyst stated "You could always tell them by their socks." Another pointed out that regular Russian embassy employees always had cheap shoes, but the intelligence agents had very nice shoes.
  • This trope is Played for Laughs (in tandem with what appears to be either Political Correctness Gone Mad or just Eagleland) in this Cold War-era joke:
    An elite American spy, after extensive and grueling preparation, is parachuted over Siberia in the dead of winter. He quickly gets rid of the parachute, dons local garment and starts to wade through the snow. After a lengthy march he finds a lonely hut, knocks at the door, and is allowed to enter by an elderly lady living in it. She invites him for a snack, and after some time asks:
    Lady: You're an American, aren't you?
    Spy: But Granny note , how could you?! Don't I speak like a Russian?
    Lady: You do!
    Spy: Am I not dressed like a Russian?
    Lady: You are!
    Spy: Don't I drink like a Russian?
    Lady: Oh, yes, you do indeed!
    Spy: Then why are you saying such things?!
    Lady: You see, son... it's because we have no Negroes.
  • This is how the Allies spotted Ernst Kaltenbrunner, the Nazi General in the SS. Kaltenbrunner gave himself up claiming to be a doctor and offering a false name. However, his mistress spotted him, and by chance occurrence, she called out his name and rushed to hug him. On 12 May 1945, this action tipped off the Allied troops, resulting in his capture, trial, and execution.
  • There are quite a few videos on YouTube of Phony Veterans like this one getting called out by actual soldiers for claiming to be part of nonexistent battalions or wearing medals improperly.
  • The English highwayman Dick Turpin was reportedly caught this way after fleeing to Yorkshire and changing his name. Dick wrote a letter to his family, but he'd been taught to write by a postman. So when that postman received the letter and realised 'John Palmer' had exactly the same handwriting as a notorious armed robber, the trail lead back to Dick and he was arrested and executed.


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