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Imposter Forgot One Detail

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"Your shuriken pouch is on your left leg, but Naruto is right-handed."
Sasuke Uchiha, Naruto

Basically, someone has been body-snatched, copied, or impersonated, but some mannerism, trick of speech, or other attribute has been lost in the snatching/copying, which inevitably gives them away as a fake. Subtrope of Spot the Impostor.

Compare to Something Only They Would Say and Bluff the Impostor. If there's a deliberate attempt to figure out if someone is an impostor, as opposed to the impostor accidentally exposing themselves, that's an Impostor-Exposing Test.

See also Cover Identity Anomaly and Spotting the Thread. Super-Trope of Eye-Dentity Giveaway in case the eyes are genuinely forgotten and not just a visual cue for audience's benefit.

Expect spoilers!


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    Anime & Manga 
  • Magical Girl Lyrical Nanoha A's: When the masked men take on Nanoha's and Fate's identities, parts of their Barrier Jackets are not the correct color. This is likely because cats, and — by extension — Cat Girls, are colorblind. Not that it really matters, since the person they were trying to fool had never seen Nanoha or Fate in their Barrier Jackets.
  • Fullmetal Alchemist: Envy does this a lot.
    • Hughes is able to realize that Maria Ross is being impersonated by Envy because she doesn’t have her mole. This doesn’t save him from being killed, nor does it save Ross from being framed for his murder.
    • Riza Hawkeye also has an encounter with Envy late in the story, and weaponizes this trope. Envy disguises himself as Roy Mustang and addresses her as "Lieutenant." She pulls her gun on 'him,' saying that she knows 'he' is a fake because when she and Mustang are alone, he calls her by her first name. Envy immediately drops the disguise out of shock, at which point she calmly announces, "I lied. Thanks for falling for it."
    • Happens when Envy fights Ling. The homunculus ends up on the ground, and as Ling gets ready to attack, Envy transforms into Lan-Fan to catch him off guard. However, Lan-Fan had recently lost an arm but, having not seen her in said state, Envy's form has two. This is still enough to rattle Ling who freezes long enough for Gluttony to launch an attack. Averted in the anime where he somehow perfectly impersonates Lan Fan in an injured and vulnerable state.
  • Naruto:
    • A Rain Ninja impersonating Naruto puts his shuriken holster on the wrong side (having a different dominant hand) and doesn’t include the cut Naruto got from Anko. Sasuke says this lack of attention to detail makes the Rain Ninja worse than Naruto.
    • Directly after this incident, Sasuke makes up a long and complicated Trust Password to serve as the one detail. Orochimaru later disguises himself as Naruto and recites the password perfectly. Sasuke immediately realizes that he's an impostor, as he forgot that Naruto was an Idiot Hero who could never have gotten the password correct on his first try (this being Sasuke's plan with the password all along). Sure enough, when the real Naruto appears, the first thing he does is ask for Sasuke to repeat the password.
    • In a filler arc, Naruto, Kiba and Hinata invoke this trope to distinguish themselves from their impostors. They have Hinata, who injured her leg, stay behind, and have the real Kiba be identified by having Akamaru with him, and the real Naruto identified by the chest via carrying it like a backpack. Amusingly enough, at the end of the arc, Naruto sets down the chest for a moment and Hinata, noticing he doesn't have it with him, sends him flying with a palm strike.
    • In another filler arc, the villains impersonate Hinata, but the fake Hinata doesn't blush when coming into contact with Naruto.
    • In the Sasuke Retrieval arc, Shikamaru disguises himself as Jirobo and pretends to catch up with the rest of the Sound Ninja Four. When Tayuya scolds him for being late, he apologizes, but Kidomaru refuses to hand over the barrel containing Sasuke, saying that Jirobo would have scolded Tayuya for her bad language.
  • In Bleach, Szayelaporro makes clones of Uryu, Renji, Dondochakka, and Pesche. Uryu and Renji’s clones’ hair is slightly different and they have markings on their eyes. Dondochakka’s clones have no spots on their backs. Pesche’s clones wear trousers rather than a loincloth. Szayelaporro claims that this is not carelessness as much as modifying them to fit his tastes, and while Renji claims he is stupid for doing this, Uryu notes that Renji didn’t notice until he pointed it out.
  • In Tsubasa -RESERVoir CHRoNiCLE-, a minor antagonist tries to protect himself from Syaoran's attacks by claiming to have taken Sakura hostage. However, Syaoran realises that the Sakura in front of him is just an illusion, since she calls him "Syaoran" instead of "Syaoran-kun". They're not on a first-name basis anymore; their past together has been written out of her memories as per the deal he made with Yuuko.
  • Pokémon: The Original Series:
    • "Ditto's Mysterious Mansion": Duplica is an on-stage impersonator and a pokémon trainer specializing in ditto. However, her current ditto can't keep up because its otherwise flawless transformation into other pokémon is hampered by its inability to match their faces. Duplica has therefore put the showbiz on pause while she and Ditto work on his facial transformation. Funnily enough, she finds that her own impersonation game could use some work when she dresses up like Ash and Brock is immediately able to identify her as a girl. With the protagonists' (and Team Rocket's) help, though, Ditto finally learns to transform fully.
    • "Imitation Confrontation": Duplica meets the protagonists again when she's busy training a second ditto and this one has the quirk that while its transformation is perfect in form, it cannot adjust its volume to match whatever pokémon it imitates. By this point, Duplica has learned to embrace imperfect transformation and looks forward to assembling a team of ditto who all transform imperfectly in their own way. As per the last time they met, Duplica's imitation game is still not good enough to fool Brock, who can readily tell that her disguise as Nurse Joy is not the real deal.
  • In Pokémon Heroes, the disguises Latias resembles Bianca (no relation), with the only difference being that Latias does not wear the white beret on her head, unlike Bianca, which she is never seen without.
  • Case Closed:
    • There is a flashback episode where a grown-up Shinichi is combating Kaito Kid (who can near-perfectly disguise himself as anyone). Shinichi figures out which police officer Kaito was disguised as because he was the only one who remembered his own I.D. number. No one remembers their I.D. number.
    • Episode 651 features the culprit being unmasked because A) he responds to a phrase that sounds like a person's name to someone who speaks standard Japanese like the Osakan Heiji and Kazuha (namely, recognizing it's a candy and telling the girls they shouldn't spoil their meals with sweets); and B) when given oversalted ramen, echoes Heiji and Kazuha's sentiments that it's "overspiced" (Osaka-ben speakers only really use the word "salty" to describe salt water and in food, call salt a spice).
    • Whenever Kid disguises himself as someone else, there's usually a little detail that gives him away. Specific examples shown here:
      • Kirin Horn: Kid disguises himself as Genta to prove he can even disguise himself as a child by hiding his legs in a hole. However, Conan sees through it when he realizes Genta's bald spot was on the wrong side of his head.
      • Trick Box: The first clue was Agasa helping Ran get a book off a high shelf, which the real one can't do because he's about the same height as her. The real key, however, was the fact the Professor didn't call Conan by his real name in private.
      • Blush Mermaid: Sera was the one who suggested the group splitting and seemed shocked that Ran and Sonoko wanted to group with her. Kid must've mistaken Sera for a guy like most people and didn't know why two girls were so close to "him".
      • Blue Wonder: Kid disguises as Suzuki and goes without his googles since it would ruin his disguise. This gave him away though: the real Suzuki wears contacts, and it's extremely painful for them to use motorcycles without goggles.
      • Green Emperor: Makoto realizes Kid was Sonoko due to him having different finger lengths from her.
      • Fairy's Lip: Conan notices Kazuha was bending her knees the whole time and called herself "uchi" instead of "atashi".
  • In Kinnikuman, Terryman attempted to masquerade as Kinnikuman to fight the Seven Devil Choujin while Kinnikuman recovered from his first bout with SteCasse King. He's quickly busted by being left-handed when Kinnikuman is right-handed.
  • Marine Boy: A false Marine Boy calls the real one's Dad by a variation of "father" the real Marine Boy doesn't use and this clues Marine Boy's Dad to the fact someone is impersonating him.
  • In Dragon Ball Z, Semi-Perfect Cell tries to lure Android 18 to him by imitating Android 17's voice. He gives himself away when he praises Dr. Gero, unaware that 17 and 18 both despise the man.
  • In a story of To Love Ru, the target of the hitman Black is revealed to be an alien and master of disguise named Karmelon, who was disguised as a boy. Not giving up, Karmelon turns into Nana, hoping to throw Black and Yami off. But Karmelon's transformation backfires, as he forgets to copy Nana's chest size, which angers Nana into beating him to a pulp.
  • In the first Sailor Moon series, the Black Moon send out a monster disguised as Chibi-Usa's mother to try tricking and capturing her. Chibi-Usa at first falls for it and almost runs into the impersonator's arms, but stopped herself and said that the impostor forgot one detail: she called Chibi-Usa "Rabbit", aka the Black Moon's name for her. Her mom Queen Serenity refers to Chibi-Usa as "Small Lady" instead. In the dub, where the villains are the ones who call her “Small Lady”, the inverse is the result
  • Bakugan Battle Brawlers has shapeshifter Zennet using her Easy Impersonation skills to transform into Julie. Dan sees through her when she acts like an Entitled to Have You bitch.
  • During the "Six Days Later" portion of the Mahora Festival arc in Negima! Magister Negi Magi, the daughter of one of the teachers at Mahora Academy tries to hinder the attempt by Negi's students to save him by, among other tricks, creating an illusion of Takahata to confront Asuna and Yue. However, Yue is able to deduce that this is not the real Takahata by the fact that he referred to her as "Ayase-san", whereas the real one, thanks to his experience of being the one responsible for the remedial sessions with the Baka Rangers before Negi arrived, would have referred to her on a given name basis.
  • One Piece: During the Arabasta Arc, one of the antagonists has the power to perfectly copy someone's appearance. When "Usopp" offers to transport Vivi to the palace on a horse after her duck mount Karoo is badly injured protecting her, she immediately realizes something is amiss when "Usopp" refers to Karoo as just "that bird" and says to leave him behind. Usopp had closely bonded with Karoo over the course of the adventure, so such callousness was very suspicious. "Usopp" tries to allay Vivi's concerns by showing her the armband they had previously established to identify one another, at which point Vivi knows for sure he's an imposter, because the real identifier was an X-mark painted under the armband.

    Audio Plays 

    Comic Books 
  • Astonishing X-Men: The X-Men travel to the Breakworld, a planet whose hat is being obsessed with killing and bloodsport to the point where having one's arm ripped off is the highest honor possible. The leaders of the Breakworld have discovered an ancient mural which prophesizes that Colossus is fated to destroy their planet, and seek to blow up the Earth in preliminary revenge. It isn't until the end of the book that Beast is able to figure out the truth: the mural is a recently-made fake deliberately designed to lure the X-Men to the planet and arrange for them to cause its destruction against their will, as Big Bad Aghanne, a healer, has grown so weary of the endless fighting on the planet that they're willing to kill everyone, including themselves, to end it. Beast explains that the mural was almost perfect, but the creator forgot to make it look as if it had been carved from primitive tools—close inspection revealed that it was made with the kind of hyper-precision that only a contemporary laser could provide.
  • Batman: In Batman: Hush, it seems like Jason Todd has returned from the grave to get revenge on the Caped Crusader. However, Batman deduces that it's actually the shapeshifter Clayface impersonating Jason—namely because he never refers to Batman as "Bruce." Jason was one of the few people in the world who knew the Dark Knight's secret identity, and Batman correctly reasons that the real Jason would use that knowledge against him.
  • In The Batman Scooby-Doo Mysteries, the Mystery Inc. gang find themselves transported into the future of Batman Beyond and aiding Terry McGinnis. While a few things ping them as odd, Velma deduces something is very off when Commissioner Barbara Gordon doesn't immediately recognize them. Turns out the entire thing was a plan by Hugo Strange to find out Batman's secret identity. When we see Terry and Bruce talking about this event in the future, Bruce also suggests that there's no way people wouldn't have recognized the real Mystery Inc. in front of them.
  • DC Comics Bombshells: Constantine tries to infiltrate the Nazis by dressing as one, but is found out because he was smoking an English brand of cigarette.
  • Fantastic Four: In 1984, this is used in a Retcon Story Arc, when the Thing's long-time love interest Alicia Masters started undergoing some changes in characterization. She soon switched allegiances from the Thing to the Human Torch, and she married Johnny Storm in 1987. In 1991, it was revealed that this "Alicia" was Lyja, a female Skrull agent. She was good enough at impersonating Alicia that none of the Fantastic Four, their allies, and most of their enemies figured out the differences. Except for the super-villain Puppet Master, who happens to be Alicia's stepfather/adoptive father and raised the girl from childhood. He could tell that his "daughter" was acting out of character and started investigating why. Forgetting that the woman she was impersonating had a parent who knew her better than anyone else, Lyja undermined a pretty good espionage scheme.
    • A key moment in the above is when the Puppet Master visits the grave of Alicia's mother to find it covered with grass, vines, and dead flowers. This indicates Alicia hasn't visited the grave in a long time which is the first true clue to the Puppet Master that something was wrong as Alicia never went a week without going there.
    • Puppet Master tricks the New Warriors into attacking the FF as a distraction so he can talk to Alicia. Truly blind as part of the disguise, Lyja reacts as if to a complete stranger which confuses Puppet Master. When the Torch arrives and identifies him, Lyja realizes her mistake as the real Alicia would instantly recognize her stepfather's voice.
  • Green Arrow (2023): Ollie learns that his bouncing around time and seperation from the Arrow Family was all arranged by an older version of him, who says this is the only way to avoid a Bad Future in which all his loved ones die. Future Ollie says he's meant to be alone; he should have died on the island and on some level he knows that which is why he never returned there. Present day Green Arrow shoots him in the eye for a Robotic Reveal and says he goes back to the island all the time, he just never talks about it.
  • Laff-A-Lympics: In "The Day the Rottens Won", Dynomutt figures out there's an impostor pretending to be Blue Falcon when he asks why Radley Crown didn't show up for the opening ceremony and the impostor, not knowing Crown and the Blue Falcon are one and the same, asks how he should know.
  • Paperinik New Adventures:
    • During one of the many attempts of the Evronians to capture Xadhoom: after identifying her as a Xerbian, they lure her to a false Xerbian colony with the intent of tricking her into wearing a restraining device, but when a happy Xadhoom mentions their party should have a Xarghon and they don't know she sees through the ruse... And amuses herself with their attempts at guessing what a Xarghon is. When the Evronians finally catch on, Xadhoom informs them that a Xarghon is a traditional Xerbian welcome dance that any Xerbian child would have known of and promptly blows them up.
    • In a less amusing instance, Paperinik disguises himself as Grigorji Grimka, son of Belgravia's president to infiltrate the country and find out who in the government had betrayed and was trying to kidnap him, but outs himself to Grigorji's arranged fiancee when he tries to be gentle with her and offers her flowers, something the real one would have never done as he doesn't like her and knows she's allergic to pollen (and would have beaten him up had he given her flowers). Luckily, the fiancee is not the traitor but one of the loyalists, and they show up for the rescue at the decisive moment.
  • Prodigy: In the Mark Millar series, super-genius Elliot Crane is recruited by CIA agent Rachel to stop an ancient conspiracy that is planning to invade Earth. Crane figures out the calculations they can use to invade via another dimension at which point Rachel shoots him, revealing she was in on the conspiracy and they were using Elliot's genius to unlock the code. Leader Tinker gloats on it all...only to realize that the "code" has given Elliot full power over their computers to destroy the invasion. When Tinker asks how Elliott knew Rachel was setting him up, Elliot responds that Rachel couldn't speak Bedouin when it was a prerequisite for any CIA agent in the area where she claimed to have been stationed. "If she was lying about that, she was lying about everything else."
  • Richie Rich: In one story, butler Cadbury is replaced by an impostor. Richie realizes the deception when said impostor calls him "Richie" instead of "Master Rich", something the real Cadbury would never say.
  • Royals: Medusa determines there's something up with Black Bolt quickly. His moodiness and distance from her isn't as much of a giveaway, because they've had problems before. But Black Bolt not even lifting a finger to help fight off attackers? That's what helps Medusa realise it's Maximus in disguise.
  • In The Smurfs comic book story "The Fake Smurf", Gargamel (and Hogatha in the 1980s Animated Adaptation) was capable of creating a formula that can change him into the form of a Smurf...but one detail that was missing in the transformation was that his impersonation doesn't have a tail. Gargamel tries to correct this by gluing a fake tail onto his behind, but later on, the tail ends up falling off, and Gargamel is soon spotted and revealed to be the fake Smurf.
  • Sonic the Hedgehog (IDW): This is a reoccurring problem for the shapeshifting Mimic the Octopus. While his disguises are mostly convincing, he always messes up some details in the way they look or act, which gives him away. For example, his impersonation of Sonic has the wrong eye color and he refers to himself as "Sonic T. Hedgehog" instead of "Sonic the Hedgehog".
  • Spider-Man:
    • In the Spider-Man: Hobgoblin Lives! mini-series, Peter and Mary Jane are conversing about Ned Leeds, the man they all thought was the original Hobgoblin. However, as they were doing so, Peter realizes something he should have had ages ago: if Ned Leeds was the real Hobgoblin, the assassins that came in and killed him would have been the ones dead because he would have had the Goblin Formula in him. That leads to everyone realizing they'd been had. Among other powers, uses of the Goblin Formula get a Healing Factor and have recovered from seemingly deadly injuries. Ironically, Ned does come back from the dead during The Amazing Spider-Man (2018), where it was revealed he did take the serum, but it hadn’t taken effect until he died.
    • In a 1990s storyline in The Amazing Spider-Man (1963), Peter Parker's parents Richard and Mary appeared to have returned years after being believed dead. All evidence indicated they'd been held prisoner in Russia and were accepted by everyone. Richard suggested they all go out to a dinner to celebrate the anniversary of May's wedding to Richard's brother Ben. May instantly knew something was wrong because while she and Ben had a public wedding on that date, they actually had gotten married first in secret a month before...and Richard and Mary had been there. This was the first clue for Peter to discover his "parents" were androids created by the Chameleon.
    • Early in The Superior Foes of Spider-Man, Boomerang figures out that the gangster Hammerhead menacing him is actually a disguised Chameleon, because Chameleon!Hammerhead was talking in a stereotypical gangster accent, and while that is Hammerhead's signature trait, the real Hammerhead had actually dropped the quirk at that point.
  • Superman:
    • This is what pings Lois Lane into realizing the Cyborg Superman isn't the real Superman in the "Reign Of The Supermen" arc of The Death of Superman - he casually mentions to Superboy that he wished he had better control of his powers when he was his age. Lois remembers that Superman didn't get his powers until he was an adult (in that continuity).
    • In the Team Superman one-shot, a villain fakes Superman deciding to leave the Earth. His motivations make sense, his disguise fools Batman and even Martian Manhunter's telepathy ... And then Lois flatly tells Supergirl it wasn't him. "He said goodbye to me with the same warmth and affection as he did Jimmy Olsen. Whoever this is did their homework, but they didn't know the secret."

    Fan Works 
  • Contraptionology!: The Cortland that speaks in Applejack's dreams is very callous about exterminating pests and unwanted things, when the real one was known for never hurting a fly and taking pains to harmlessly relocate crop pests.
  • In the Fresno, California-based Doctor Who Audio Dramas' continuity, the David Segal Doctor traveled with mute reporter Susie Jo Parker. Although mute, Susie Jo did speak. Usually when an impostor took her place and didn't research her very well.
  • In White Devil of the Moon, the impostor, posing as Reinforce, referred to Hayate and Signum as 'the two of them' when the real Reinforce would have noticed that Signum was in Unison form, indicating the presence of a third person.
  • In A Far Cry from Home, Faith Seed tries to seduce Pagan Min into joining the Project at Eden's Gate by using her Bliss drugs to make him see her as his long-dead lover, Ishwari Ghale. She nearly succeeds, but then she botches it up by saying to Pagan, "Please, come with me, my darling."
    Pagan Min: Love.
    Faith Seed: What-
    Pagan Min(grabbing Faith in a Neck Lift): Ishwari called me, "my love." She was very particular with her words.
  • In the Pony POV Series, Twilight attempts to repair Trixie's broken psyche, only to find herself with a psychiatrist who claims that she suffered a severe mental breakdown after accidentally killing Trixie completely and dragging the corpse around pretending it was still alive. Twilight starts to have suspicions when the doctor tells her that her "three friends" dumped her there, and moreso when the doctor can't understand why Twilight would think the Princess would care about this. Twilight is actually trapped by Trixie's subconscious, and Trixie never met Fluttershy or Pinkie, nor did she know about Twilight's official position.
  • In Ojamajo Doremi: Rise of the Shadows, the Queen is able to figure out that it's not Majorin whom she's talking to but rather her Shadow, Evil Rin. She figures this out because Shadows in this fic do not cast shadows of their own. That, and she noticed something "off" about "Majorin's" behavior.
  • In Waking Nightmares, Soldier, Derpy, Dinky, and Amethyst Star get replaced by changelings. The deception lasts less than a day before the protagonists wisen up to the inconsistencies (because the real Soldier never calls Spy a pervert [coward, sometimes maybe, but not pervert], Derpy hates English muffins, and Amethyst hates the Doctor due to some unspecified incident) and lead the imposters into an ambush.
  • In Shadowchasers (Cyber Commander), Jinx is looking for the shapeshifting boggart in a wax museum (an incredibly dangerous situation, like looking for a needle in a haystack and the needle is trying to kill you). However, when she passes by a display representing the duel between Obi-Wan and Darth Vader in A New Hope, she notices that the Darth Vader statue has a green lightsaber, and realizes that must be him.
  • In Shadow Realm PI, a fic set in the world of the Duel Monsters cards, someone frames the Amazoness monsters for her crimes by attacking people using an Amazoness Blowpiper's blow darts. One of her surviving victims realizes she was a fake because she was wearing high heels while the Amazonesses go barefoot.
  • In Fly Me To the Moon: A Buffy Bayonetta Tale, Luka impersonates a soldier named Curtis to infiltrate a military base, taking great pains to look just like him and imitate his voice and mannerisms. Riley Finn spots him because his hands are smaller than Curtis' and perfectly smooth and manicured. Curtis fought and handled firearms his whole life, leaving his hands huge and calloused.
  • In Equestria Girls: Friendship Souls:
    • Grand Fisher attempts to lure in the Pie family by making his lure look like Pinkie Pie. Maud sees through it because "Pinkie" mentions she abandoned her friends to save herself from the Hollows, which Pinkie would never do. Maud also claims her scent is wrong.
    • Acknowledged by Hoity Toity while masquerading as Sour Sweet, as despite changing his appearance and having Sapphire Shores change his reiatsu signature he knew he doesn't know nearly enough about Sour Sweet's personality and mannerisms to 100% act like her. However, he takes advantage of the fact none of the Shadowbolts or Twilight really know all of Sour Sweet's quirks down pat like True Companions should to make the deception work.
  • Inaccurate Legends: The Witch tries to trick Shirou and Saber into serving her by impersonating God, but when she orders them to kneel and grovel, Saber remembers that God doesn't like people worshiping him like that.
  • Two assassins attempting to kill the Goblin leader in The Awakening of a Magus attempt to enter his office in Gringotts under the guise of Ludo Bagman captured by Albus Dumbledore. However, while "Albus" speaks Gobbledegook, he didn't bother to learn the proper gestures required, nor can he replicate Dumbledore's eye twinkle properly. Of course, the actual first hint the Goblins get is that the real Dumbledore is already in Gringotts on official business.
  • Stargazer: At the end of chapter 46, an Ahamkara tries to pull a Shapeshifter Guilt Trip on Ikharos by transforming into Eris. While this does initially make him hesitate, when Ahamkara!Eris tells him that she wants to apologize, he cuts her off mid-sentence via a bullet to the head. He then remarks that the real Eris would never say sorry for anything before emptying his entire magazine into the corpse.
  • In The Witch of the Everfree side story Don't Invite Witches to Weddings, Sunset Shimmer seemingly falls for Queen Chrysalis' Cadance disguise... only for the unicorn to bluntly reveal that her magic color was wrong. Chrysalis has an acidic green aura, Cadance's is an icy shade of blue. Cut to Chrysalis bursting into Celestia's office in a panic, chucking a still bound-and-gagged Cadance at her hooves, begging for sanctuary from Sunset's wrath, and then self-defenestrating when she doesn't get it. The whole thing is Played for Laughs.
  • Naru-Hina Chronicles Mini-sodes: Nanami decides to get Naruto's attention by disguising herself as Hinata. When she tries to convince him to go with her to some hotel, he's not fooled at all and tells her she didn't quite get Hinata right, although without elaborating about it. For one thing, Nanami didn't have the Hyuga's Byakugan eyes (it looks like she didn't think about having any contact lenses that would give the impression she has those eyes), but she also acted in a much bolder way than how Hinata would usually behave.

    Films — Animation 
  • Near the end of Aladdin The Returnof Jafar, at the very beginning of the final battle against Jafar, when Jafar, now transformed back into his genie form tries to strangle Aladdin, "Aladdin" turns out to be the Genie in disguise, with the fake Aladdin now wearing a fez on his head, unlike the real Aladdin.
  • In Barbie as the Princess and the Pauper, Preminger, who abducted Princess Anneliese, writes a letter from her claiming she ran away and goes as far in the detail as to perfume the letter with lilac. However, her tutor Julian happens to know she wouldn't use anything other than rose.
  • Barbie Fairytopia: In "Magic of the Rainbow", Laverna kidnaps Sunburst and disguises herself to look like her halfway through the movie to destroy the Flight of Spring. When Sunburst questions Elina at the end how she was able to find out Laverna was disguised as her, Elina's simple reply was, "Laverna was nice to me."
  • Dreambuilders: How Minna learns that her "mother" is actually a Dreambuilder in disguise: she suggests that the two stay and play board games, whereupon Minna points out that her mother hated board games.
  • Leroy & Stitch: After Stitch has been kidnapped, Leroy shapeshifts himself to look like him to throw Lilo off as she contacts him. However, Lilo sees right through the disguise when she points out Leroy is not wearing the tiki necklace she gave Stitch prior to his departure from Earth, and realizes Stitch is in trouble.
  • In Megamind, Megamind blows his cover in one scene by pronouncing Metro City to rhyme with "atrocity." He just barely avoids doing the same earlier in the film.
  • Subverted in Toy Story 3. Barbie uses an astronaut suit to disguise herself as Ken to talk with the Bookworm. The suit covers her head and face, and almost her whole body...except her feet, and she forgot to change her high heels, which the Bookworm sees as she walks away. Fortunately, the Bookworm dismisses the high heels as one of Ken's idiosyncrasies.

    Films — Live-Action 
  • The 14 Amazons: General Chiao, The Big Guy, managed to infiltrate the Mongol army's camp by donning disguises from a burly Mongol mook he killed, on a scouting mission for the Yang family army which he serves. Unfortunately, he's still wearing his own boots - Mongol soldiers prefer wearing pointy-toed boots, unlike members of the Yang army.
  • In The Sorcerer's Apprentice, sorcerers powerful enough to do so have the ability to morph into whomever they wish. When Drake Stone, a less experienced Morganian, attempts to trick Balthazar into giving him the Grimhold while disguised as Dave, he accidentally lets his British accent slip, giving himself away. He also forgot a second detail: the black nail polish on the nails... which confirmed the falseness of the imposter!
  • In the movie Dead Again, a man claims to be the fiancé of an amnesiac woman and he presents a glove as proof. The glove seems to match the one the woman already has — a bit too well: it's for the same hand.
  • Friday the 13th Part V: A New Beginning: Roy Burns does do a good job at imitating Jason Voorhees... except for the small detail that his mask has blue accents, not Jason's red.
  • In The Thing (2011), this is how Kate realizes that Carter has been infected at the end of the movie. The Thing cannot replicate metallic objects and Kate knew from earlier in the film that Carter wasn't assimilated because he was still wearing his earring. The Thing gets wise to its weakness by the end and thought to put the earring back on after killing Carter off screen, but put it on the wrong ear.
  • In The Gumball Rally Kandinsky and Avila (two LAPD officers who are members of the titular clandestine race) have a plan to prevent police scrutiny, which is to disguise themselves and their patrol car to look like the police of every state they pass. This plan hits a snag when an Arizona patrolman notices that the car they are using (a Buick Skyhawk) is not the one the Arizona police uses (Dodge Polaras) and pulls them over. They end up having to pretend on the fly that they are part of a film crew and ask the officer to stand still and smile to the "camera" while they drive off to avoid being arrested.
  • After killing the Big Bad in Total Recall (2012), Doug wakes up in an emergency vehicle with Melina holding his hand. He then notices that she's missing the bullet wound scar on her hand, forcing his "wife" Lori to reveal herself (using a holographic device he used earlier) and attack him.
  • Invoked Trope in the 1977 version of The Man in the Iron Mask. Minister Fouquet is confronted with King Louis and his identical twin dressed exactly the same, except his sash is the wrong color (a detail the conspirators changed so they'd know who their man was) so Fouquet has him arrested. He's the twist—the conspirators knew Fouquet was on to them, so arranged for him to be told earlier that the king had changed his mind about the color of his sash. Fouquet has actually arrested the real king.
  • In The Master of Disguise during the climax, Devlin caught Pistachio in disguise as a henchman because he was still wearing part of his previous "Cherry Pie Man" disguise. That and he knows the henchman is not married. Earlier, he almost manages to fool Devlin's Mooks by pretending to be a Quint-like fisherman, but then they notice that his arms are extremely hairy, just like the man they were just chasing.
  • Though they're not impersonating one person in particular, Hicox in Inglourious Basterds gives away that he's a British spy by the way he gestures to the bartender for three more drinks. A true German would have used his thumb, index, and middle finger to denote three, while the Englishman uses his index, middle, and ring finger. Major Hellstrom picks up on this, and a Mexican Standoff begins.
  • In Wild Wild West, Artemis Gordon has a nearly foolproof disguise as President Ulysses S. Grant (the fact that the same actor plays both helps) but West quickly knows it's not Grant because he was wearing the wrong school ring (Gordon was wearing a Harvard ring whereas the real Grant attended West Point). It doesn't help that "Grant" keeps going on and on about how great an agent Gordon is.
  • James Bond:
    • In From Russia with Love, Grant pretends to be a British agent but consumes red wine with fish, something a Brit would never do. He also says "Cheero" instead of "Cheerio". Bond doesn't put two and two together until after Grant gets the drop on him, then curses himself for missing it.
    • In Thunderball, Colonel Jacques Bouvar Disguised in Drag as a rich widow. Bond spots him when he opens his car door himself instead of waiting for the chauffeur to do it.
    • In You Only Live Twice, Bond disguises himself as an astronaut but is spotted by Blofeld when he tries to carry his air conditioner unit onto the spacecraft he's boarding.
    • In On Her Majesty's Secret Service, James Bond impersonates Sir Hilary Bray in order to operate as a mole on Blofeld in a mountaintop clinic. Bond is caught when he says the Bleuchamp family crypt was located in St. Anna's Kirche, not in the Habsburg cathedral—which, as Blofeld notes, Sir Hilary should have known. Blofeld also comments that professional baronets who are getting paid good money for their work would not have seduced all the women in his clinic.
  • The Dark Side of the Moon (1990): Satan apparently forgot or didn't care that his host body is allergic to sugar in his coffee. It's down to just two crew members by that point, so the only remaining human immediately starts to prepare for the final confrontation.
  • Narrowly subverted at the end of The Last Jedi. When Luke sends an Astral Projection of himself to aid the Resistance on Crait, he has his doppelganger wield the blue Skywalker lightsaber - a detail which would have given him away to Kylo Ren, who along with Rey had accidentally destroyed that weapon at the end of the film's second act. However, Kylo did not notice this at all, likely because his rage towards Luke got in the way of his rational thinking - and this is exactly what Luke wanted, exploiting Kylo's rage to buy the Resistance enough time to escape Crait. Luke presumably used a projection of his blue lightsaber just to troll Kylo, knowing he would recognize that detail only after Luke's ploy was exposed.
  • Captain Marvel (2019): The Skrull Talos impersonating Director Keller gives himself away when he calls Nick Fury "Nicholas" instead of Fury.
  • Last Days of Mussolini (1974): German troops try to smuggle Mussolini through a partisan checkpoint by dressing him as a German soldier, but he's still wearing the trousers of a high-ranking officer.
  • In The Bold Caballero, the Commandante plays Costume Copycat and attempts to frame Zorro for the murder of the Governor. However, being only semi-literate, he carves the Zorro Mark backwards: an 'S' rather than a 'Z'.
  • Undeclared War: A conference between several ambassadors and political figures are to be blown up by terrorists using a Time Bomb hidden in a flower basket, but the police manage to learn of the attack beforehand and quickly orders for the meeting location to be changed upstairs. One of the terrorists, disguised as a security officer, tries moving the flower basket upstairs as well, prompting CIA Agent Gary Redner to question where he's moving the flowers. Said terrorist claims that he's taking the flowers back as an anniversary present for his wife, but Redner shoots him after realizing he doesn't have a wedding ring, revealing the ticking time bomb in the basket in the process.
  • Hollow Triumph: When Johnny assumes Dr. Bartok's identity, he needs to scar his cheek. However, working from a photograph printed from a reversed negative, he applies the scar to the wrong side.
  • In The Man Who Changed His Mind, Dr. Laurience transfers his mind into Dick Haslewood's body. However, he doesn't know that Dick doesn't smoke, so when Dr. Wyatt sees him chain-smoking she realises the truth.

  • In Maximum Ride, the clone meant to replace Max has little knowledge of the flock, which means she doesn't know that Iggy is the Team Chef despite being blind, while she is supposed to be a terrible cook. Her cover is blown by the fact that six-year-old Angel is a mind reader, and was never fooled in the first place.
  • This is the Fatal Flaw of the main antagonist of Needful Things. He cooks up fake evidence of crimes or slights and then plants them on people to turn them against each other, but he keeps getting small details wrong, either out of arrogance and negligence or maybe for sport. For instance, the town's sheriff is shown an illusion of the death of his wife and child being due to a local hoodlum (in order to make him try to kill the man). The sheriff realizes it's a fake when he notices that they're wearing their seatbelts in the illusion - when not wearing them was what killed them in the first place.
  • A Song of Ice and Fire:
    • The Faceless Men, a guild of master assassins, disguise their identities by a combination of glamour magic and acting skills. Part of their training, therefore, involves completely rejecting all traces of one's real identity, including name, family, and personality. Arya Stark is told off every time she gives herself away with the Character Tic of chewing on her bottom lip.
    • Another Faceless Man was impersonating a poor student of the Oldtown Citadel. This student had a pet peeve: he hated being called a "pig boy", after a fairy-tale character of the same name as him. The Faceless Man, while introducing himself as that student, makes the mistake of calling himself "like that pig boy".
  • In Allen Steele's The Tranquility Alternative, one of the first cracks in the imposter's assumed identity is when he doesn't respond appropriately to an elaborate online *cough* "roleplaying" scenario - such as not knowing that his virtual lover's fictional husband was killed off years ago. (An author's aside notes that the original would have told his captors anything they wanted to know... but they never thought to ask.)
  • In the Ciaphas Cain short story The Little Things, Cain's first clue that the "waiter" bringing dinner to Amberley's hotel suite is a fake comes when he pounds loudly on the door — a room service waiter in a high-class hotel should have tapped politely. Finding that the man's uniform doesn't quite fit right — when everyone else on the hotel's staff was wearing professionally tailored outfits — just confirms it.
  • In one of Aesop's fables, a literal Ass in a Lion Skin accidentally outs himself by braying. In another one, A Wolf in Sheep's Clothing accidentally outs himself by howling (although in other versions, the disguise works too well and he ends up slaughtered for food by the shepherd).
  • In Going Down for the Count by David Stukas, the eponymous Count Siegfried von Schmidt has blue eyes and is an utter bastard. Manfred Weber, the man hired to impersonate and murder the count, has green eyes and is charming and romantic. Unfortunately for Manfred, the plan requires him to seduce hopeless romantic Robert, which he cannot do while better emulating the count, and the optometrist from whom Manfred purchased his color-changing contacts ends up mentioning the purchase to Robert. The discrepancies lead to Manfred and his employers being caught.
  • Agatha Christie plays with the trope sometimes.
    • This proves to be a fatal flaw in After the Funeral, a Hercule Poirot novel. When Richard Abernethie dies, his family gathers for the funeral and reception, at which point Cora Lansquenet, a relative, remarks "But he was murdered, wasn't he?" The next day, Cora herself is found dead, prompting the police to think that she was killed because she knew about the plot to murder Richard. Poirot himself begins investigating; all the while, Helen Abernethie is troubled by something that happened during the reception, but can't quite figure out what it is. Both she and Poirot eventually realize the problem—Cora was known for twisting her head to the right when she asked probing questions, but at the gathering, she tilted her neck to the left. It turns out that the "Cora" at the funeral was really her housekeeper and murderer Mrs. Gilchrist; she was trying to create the false impression that Richard was murdered to throw suspicion off herself. Unfortunately, she practiced her Cora impression in a mirror, and thus inadvertently reversed all of her motions.
    • In a Poirot short story The Veiled Lady, a member of a criminal gang wears smart and expensive clothes, but her shoes are old and cheap. That leads to Poirot fighting out she’s not a noble if impoverished lady she pretends to be.
    • In the short story Jane in Search of a Job, the heroine is hired to act as a double for a Grand Duchess. She looks extremely like her and she can even speak French… but she is one inch shorter and has to wear high heels, while the Duchess wears low heels. It doesn’t end badly for her, though.
    • In another Poirot short story "Four and Twenty Blackbirds" a murderer is able to maintain a perfect impersonation of his victim at a restaurant in order to establish he was still alive at a given time. However, he ordered the food he liked, not that of the victim, and the waitress noticed the discrepancy and mentioned it to Poirot.
  • In the first book of Codex Alera, Fidelias figures out that a slave girl was really Lady Aquitainus Invidia because, even though she was shapeshifted via watercrafting, her body language was far more calm around Lord Aquitainus Attis than would be expected of an actual slave girl.
  • In the Hand of Thrawn duology, Moff Disra comes up with a plan to make it appear as if Grand Admiral Thrawn is still alive in order to run The Remnant from behind the scenes. To this end, he, a Con Man named Flim (disguised as Thrawn), and a former Imperial Guardsman named Grodin Tierce present Flim as Thrawn, who manages to fool anyone he meets thanks to preparation and his skills as a grifter. In fact, Tierce gambles on one of the officers to secretly take a DNA sample from "Thrawn" in order to verify his identity from the official source. Apparently, Disra and Tierce have already replaced the official sample with Flim's (strangely enough, no one thinks to do a genetic analysis to see if the sample is Chiss, since Flim is human), so they aren't worried. Except it turns out that there is another genetic repository located in the Uncharted Space, hidden away by Thrawn.
  • In Clive Cussler's novel The Mediterranean Caper, hero Dirk Pitt confronts shipping magnate turned drug kingpin Bruno Von Till in the climax. Pitt shocks everyone by revealing how he's discovered that Von Till is actually Admiral Erich Hiebert, a wanted Nazi war criminal who murdered the real Von Till and took his place to hide from investigators. After being arrested, Von Till is confident that nothing can be proven. What gives him away? His scalp. Hiebert had simply shaven his head bald, unaware that Von Till lost all his hair to a genetic disease. The peach fuzz on his scalp was the first clue the war crimes investigators needed to figure out his true identity.
  • In A Study in Emerald, Neil Gaiman's take on a Sherlock Holmes story, the detective investigating the death of an Eldritch Abomination in an altered Europe traces the murderers to an acting company in the London underground. To infiltrate the group, he pretends to be a theatrical promoter offering fame and fortune to the bunch, arranging for the lead actor to arrive at his flat in Baker Street the next morning to sign the paperwork (and hopefully walk into a trap). The next morning, the actor sends a message to the detective, explaining that he saw through the disguise when the sleuth pulled out a pipe and asked for some tobacco (a piece of evidence linking the thespian to the crime scene)—a brand-new, unused pipe, which a prevalent smoker certainly wouldn't be using. Given that in this universe, the "villainous" actor is Sherlock Holmes and the "good" detective Professor James Moriarty, it's less surprising than you'd think.
  • In Harry Potter and the Goblet of Fire, Dumbledore immediately realizes that "Moody" is an impostor because he takes Harry away from the Quidditch field. It's ostensibly to get him out of the crowd so he can breathe, but as Dumbledore remarks, "The real Alastor Moody would never have removed you from my sight... The moment he took you, I knew - and I followed."
  • The Innsmouth Legacy. Audrey notes how FBI agent Ron Spector is never Distracted by the Sexy (because he's a closet homosexual). In Deep Roots, she realises that he's been replaced by a doppelganger because of this trope. The problem is they can't afford to reveal how they exposed him, so the fake Ron is able to convince the other FBI agents that they're imagining things (as the doppelganger has all the memories of the real Ron Spector).
  • Ben Snow: In "Banner of Blood", the killers plan on Faking the Dead by killing a stooge and leaving his body too mangled to be identified except for the tattoo of the American flag on his chest. However, they slip up because when they take their patsy to be tattooed, the tattooist tattoos the current American flag, and two states had been added since the killer had his done.
  • Mistborn: The shapeshifting Kandra can easily Kill and Replace almost anything human-sized, except for their hair, which they have to transfer over one hair at a time. In Wax and Wayne, Wayne muses that they could spot a Kandra in a hurry because it wouldn't have hair on its... arms.
  • A Donald Duck Little Golden Book called Donald Duck, Private Eye casts Donald as a detective looking for Minnie Mouse's missing jewelry box. After being recognized by Pete while searching for the jewelry box, Pete suggests that Donald disguise himself so he doesn't draw attention to himself as he searches. In order, Donald disguises himself as Daisy Duck, Grandma Duck, and Scrooge McDuck, but each time, Donald's friends see through his façade almost immediately because he forgets one detail when disguising himself as the other three ducks: First, Daisy's eyelashes, then Grandma Duck's shoes, and finally Uncle Scrooge's spats.
  • In the Wayside School books, a Voice Changeling named Mr. Gorf comes to Wayside School to get revenge on the kids for killing his mother, the Sadist Teacher Mrs. Gorf. The lunch lady Miss Mush figures out something is wrong when Mr. Gorf uses resident Jerkass Kathy's voice to tell Miss Mush to have a nice day.
  • In The Fourth Protocol, the head of the British SIS Sir Nigel Irvine identifies a Soviet double agent posing as an Afrikaner diplomat and running a False Flag Operation to get mid level bureaucrats with sympathies to South Africa to give up secrets to him. Irvine finds old photographs of the diplomat playing cricket at university and notices that he’d played as a left arm spinner. But the man claiming to be the diplomat is right handednote . Irvine eventually outs the diplomat as a German communist agent who had killed and assumed the identity of the Afrikaner long ago.
  • The Sandman: The Dream Hunters: The monk immediately clocks that these warriors trying to intimidate them are the work of a badger, because while the magick is otherwise spotless, the last horse's tail is that of a badger. He's right.
  • Playing for Keeps: Colette's apparently useless superpower is being a Supreme Chef who instinctively knows a person's favorite food and how to prepare it just how they like it. But it turns out that this gift naturally includes the ability to immediately detect shapeshifters: they can look and sound exactly like somebody else, but they can't change their personal culinary tastes, and since that's what Colette picks up on, she instinctively spots imposters.

    Live-Action TV 
  • In The Adventures of Superman episode "Tomb of Zaharan", Clark notes that a telegram supposedly written by Lois and Jimmy did not use reporter's phrases.
  • In the season two finale of Alias, Sydney offers Francie - or rather Allison, the spy who was turned into a double of Francie before killing her - coffee ice cream. "Francie" accepts, confirming Sydney's suspicion that she isn't Francie (who hated the stuff). All hell proceeds to break loose.
  • Bewitched: In "The Crone of Cawdor," Darrin prepares to work with Terry Warbell, an attractive young woman who heads a fashion line; after he goes to work, an elderly woman shows up in the Stephens' neighborhood claiming that she's the real Terry. Endora gets suspicious and disguises herself as an employee at McMann and Tate, Darrin's company, to talk to Terry about the latest clothing trends. When Terry gives hopelessly outdated answers, Endora correctly deduces that she's the titular Crone, who has swapped bodies with the actual Ms. Warbell—the Crone of Cawdor may look the part, but she forgot to research what Terry actually does for a living.
  • On Buck Rogers in the 25th Century, Buck is suffering from a fever that alters his brain chemistry so he can see that a group of human-looking ambassadors are actually reptilian aliens. No one else believes him but the aliens realize killing Buck after the accusations will be suspicious so they alter the frequency of the device creating their holographic disguises so when his fever passes, even Buck assumes he was hallucinating. However, the aliens forgot to tell their inside agent on a space station to alter his device so when Buck saw him in his alien form on a monitor, he realized what was happening. He then lowers the ship's temperature, which is cold for humans but outright freezing for the lizard-based aliens, causing them to collapse and reveal their true forms.
  • In the "body swap" storyline of Buffy the Vampire Slayer, Buffy had Faith's Bostonian accent on certain words. (No one really noticed in-universe.)
  • In one episode of Car 54, Where Are You?, a gang of thieves had attempted to steal a large gold shipment and tried to smuggle it out of the warehouse it was hidden in by disguising themselves as NYPD officers. They would have succeeded but for one detail. They wore summer uniforms and then committed the robbery on the day that the entire police department switched to the winter uniforms.
  • Dead Man's Gun: In "Death Warrant", John Pike kills one of the Carnival of Killers pursuing him, swaps clothes with the dead man, and smashes his face in with a rick to make it look like he had been killed. However, Joe Rule, who finds the body, isn't fooled because Pike neglected to swap guns with the dead man.
  • Doctor Who:
    • "The Chase": The robotic Doctor refers to Vicki as "Susan", not knowing the Doctor has a new teenage companion.
    • "The Faceless Ones": Jamie is captured by the shape-shifting Chameleons and replaced with an impostor — who does not have the real Jamie's Scottish burr.
    • "The Evil of the Daleks": Two telesnaps from episode six show that this trope applied. When the Doctor names the three Humanized Daleks (using the Greek alphabet), he draws the lowercase letters on their shells. So when a Dalek bearing an uppercase Omega turns up, the Doctor knows it's a trap.
    • "The Android Invasion": The Doctor can tell Sarah is an android because the android Sarah is wearing a scarf while the real one wasn't (he's carrying her scarf in his coat pocket), and real Sarah hates ginger beer, yet the imposter accepts some when he offers it to her.
    • "Terror of the Vervoids": Hallett disguises himself as a Mogarian as part of an investigation, but the Doctor figures him out from one tiny slip-up: he doesn't turn his voice translator on before he speaks, and its light is off the entire time, showing that it wasn't switched on in advance. The discrepancy is so subtle that the present-day Doctor, who's using footage of the story as part of his defense while on trial, actually has to run through the scene again to show the court how he figured it out.
    • "New Earth": Lady Cassandra uses a psychograft machine to take over Rose Tyler's body. Aware that she doesn't sound like Rose, she asks her assistant Chip how she should speak to the Doctor, to which he replies "Old Earth Cockney". She manages to fool the Doctor for a while, only outing herself when she shows a Lack of Empathy towards the other patients in the hospital, something that Rose would care about.
    • "Tooth and Claw": The Doctor and Rose accidentally end up in the Scottish moors. The moment he realises they're in Scotland he switches to a Scottish accent (though not David Tennant's natural Scottish accent) and pretends to be a Scottish physician named Dr. James McCrimmon so that Queen Victoria doesn't shoot him. During the werewolf attack, he slips back into his normal Estuary English, which isn't unnoticed by Victoria.
    • Downplayed in "The Poison Sky". The Doctor immediately notices that Martha has been replaced by a Sontaran-bred clone, but the differences are so tiny, no-one without his bizarre alien senses and memory would pick up on them. He pretends not to notice because the Martha clone is doing things that work to his advantage.
      The Doctor: Reduced iris contraction, slight thinning of the hair follicles on the left temple, and... frankly, you smell. You might as well have been wearing a T-shirt saying "Clone". Although... maybe not in front of Captain Jack.
    • "Spyfall": "O" comments that he's always been a terrible sprinter. The Doctor immediately gets suspicious, as his file says he's a champion sprinter. He is actually The Master, who killed the real O on his first day and took his identity to infiltrate MI6.
  • Eerie, Indiana: In "No Brain, No Pain", after accidentally switching bodies with him, Eunice Danforth pretends to be Marshall and promises to give Dash X $1,000 if he stuns her old body with Marshall's mind inside of it. Dash is willing to go along with this plan until he realizes that the real Marshall doesn't have $1,000.
  • In The Flash (2014), when Zoom has invaded Earth 1's Central City with an army of criminal meta-humans from Earth 2, Cisco and Caitlin try to trick the army's leader Black Siren (Laurel Lance's double) by pretending to be their villainous doubles (both already dead by that point) Reverb and Killer Frost, respectively. This appears to work, at first, then Black Siren tosses a random object at Reverb, and he catches it. Black Siren explains that the people of Earth 2 have the opposite dominant hand from Earth 1, and "Reverb" has caught the object with the wrong hand. Cue the Oh, Crap! from Cisco and Caitlin. This is the first and last time this is referenced or mentioned, especially with the addition of multiple alternate Earths, where this distinction wouldn't make sense. Averted with the Black Siren herself, who is freed by Prometheus in a later Arrow episode and successfully impersonates the Earth 1's Laurel. While Felicity has suspicions, there's nothing about "Laurel" that gives her away. It's not until she remembers that S.T.A.R. Labs has the Black Siren in the Pipeline that she realizes who the impostor is, at which point the Siren attacks, glad to be finally rid of the masquerade.
  • The Good Place: Jason spots Bad Janet as an impostor because when he said "I got you, girl" she didn't respond "Not a girl", which the real Janet would have.
  • Haven: In season one's "As You Were," a shapeshifter decides to Kill and Replace Audrey at her own birthday party. Nathan figures it out after he is suspected of being the imposter, and Audrey is the one to untie him after he is cleared. The Chameleon didn't know that Audrey is immune to the Troubles, which means Nathan can feel her—and only her. He tests his theory by kissing her, which confirms his suspicions and exposes the Chameleon as the imposter.
  • In the K.C. Undercover three-parter (or four-parter, depending on where you see it, as the hour-long first part was shown internationally as two half-hour installments) "Double Crossed," K.C. has been kidnapped and substituted with a double as part of a revenge plan against Craig and The Organization. Marisa is the first to see something suspicious with her best friend when K.C. actually likes the idea of going to a party. Then, when K.C. mentions having something to do, Marisa asks if it's a spy mission, the impostor expressing surprise Marisa knows about her being a spy and Marisa realizes this isn't the real K.C. although she herself is snatched before she can do anything. The Coopers themselves find out when J.U.D.Y.-recorded surveillance footage reveals K.C. - a fervent vegetarian - eating meatballs. When the Coopers find K.C. and her double, the double tries to "prove" she's the real deal by relating a childhood story about K.C. However, that just proves she's the fake as the Coopers know the real K.C. was totally embarrassed by the incident and vowed she would never tell that story to anyone.
  • In the Law & Order: Special Victims Unit episode "Zebras", Stuckley had ambushed and held Stabler hostage. When his cellphone goes off, Stuckley answers it and tells Benson, who is on the other end, that Stabler went out to get sushi. This causes Benson to come to Stabler's rescue because she realized that Stabler would never get that because he hates raw fish.
  • In an episode of The Librarians, Stone finally reveals that he's a genius to his father, who never forgave him for leaving the family oil drilling business. His father gives him a heartfelt hug. After a moment, Stone explains that his real father would rather die than do something like that and jumps with the shapeshifter into a hole.
  • Lost Girl:
    • Inari shape-shifts into Kenzi and impersonates her after kidnapping the original. Bo exposes her after she casually eats peanuts, which Kenzi is allergic to.
    • In season 5, Hera takes over the body of a dead man, returning to visit his wife. At first, it seems the wife believes in it when Dyson comes in (having seen the man dead already) and pressing Hera on her true identity (although Dyson does at first think it's Zeus instead). The wife comes in to offer a bag of marshmallows which Hera starts downing. She/he then grabs the wife by the throat and boasts about killing her before Dyson's eyes... only for the wife to stab Hera with a shard of glass she'd pocketed before. "My husband hated marshmallows."
  • The Magician: In "The Illusion of the Stainless Steel Lady", a reclusive movie star (who is an old friend of Tony's) is being held prisoner in her house by a gang of crooks who are bleeding her bank account dry. When Tony investigates, he is shown into the bedroom of an impostor who summarily dismisses him. However, while in the bedroom Tony spots a packet of cigarettes. Tony's friend doesn't smoke and won't allow people to smoke around her.
  • An episode of Medium has a con artist finding the unpublished autobiography of a rich man. He decides to use the details of it to fool the wife into thinking he's her husband, having his spirit reborn into the body of a recently dead man, using the past details to make it work. What undoes it is how the real husband neglected to mention a few things in his biography...such as the tiny detail he was having an affair with his sister-in-law.
  • Nicely done in Merlin (2008) when Morgana resurrects Lancelot from the spirit world, brainwashes him, and sends him to Camelot in order to stir up trouble. However, Merlin catches him out by phrasing a sentence that casually references the use of magic - Lancelot being one of only two people in Camelot who knows that Merlin is a warlock. But because Morgana doesn't know, then fake!Lancelot doesn't know either, and he responds in a manner that makes no sense from one who should be aware of Merlin's secret.
  • Monty Python's Flying Circus has a sketch where a mousy little man enters the police station to surrender on the grounds that he's Atilla the Hun. The sergeant gives him a "Hunalyser" in which to blow. Nothing happens, which exposes the man as Alexander the Great. He was unaware he was blowing into an Alexander the Greatalyser.
  • In the Murdoch Mysteries episode "The Ministry of Virtue", a Mail-Order Bride who killed the charity worker who brought her to Canada poses as the charity worker, shocked to discover the bride committed suicide. While the suicide thing is quickly exposed, she does an excellent job of portraying herself as a deeply religious and rather self-righteous woman, whose only concern is to catch the train so the other brides can reach their virtuous marriages until Murdoch gives her an Ironic Echo of a Bible passage a bellhop says she gave him in lieu of a tip, and she doesn't recognise it.
  • Tested in MythBusters when Adam and Jamie tried to disguise themselves as each other - despite much effort, vocal cues and accents ended up being the weakest part of the ensembles. Adam did better impersonating Jamie than Jamie did impersonating Adam, in part because Adam frequently mimics Jamie for amusement. That may have worked against Adam, however; while his impression of Jamie was better, it had also been used on-camera in the past, so the test subjects were more likely to recognize the "Jamie" voice as an impersonation by Adam.
  • In Once Upon a Time in Wonderland, Jafar took Alice's father captive and asked for all sorts of information to better impersonate him, but hadn't seen that he prayed over every meal, however small. Once Alice sees the person she thinks is her father not saying grace when she and the Knave prepare some food, she's tipped off that something is wrong.
  • One episode of Painkiller Jane had Jane imprisoned in an institution in a plot involving a shape-changer and rescued by friend Maureen. However, when changing clothes, Jane saw that "Maureen" was lacking a recent tattoo. Jane then forgave Maureen for sleeping with a classmate back at the FBI Academy, Maureen accepting the apology and since the guy had actually been the class geek, Jane knew this was a fake. The scheme is to trick Jane into exposing her team's HQ and when they drive up to a simple house, the imposter is confused. Jane then smiles "what's the matter? You don't recognize your own house?" The imposter realizes he's found out just as the real Maureen shows up to capture him.
  • In the premier episode of The Player, this happens multiple times. Kane spots an assassin dressed as hotel staff because he's wearing the staff jacket but not the right pants. At the end of the episode he realizes it's not his wife's body in the morgue when he goes to place her wedding ring on it as the corpse doesn't have the ring tattoo around her finger that his wife had. No one else knew about the tattoo because it was hidden by the actual ring which she always wore.
  • The Adaptation Expansion of The Affair at the Victory Ball in Poirot has it as the ultimate clue that leads to the murderer’s arrest. The murderer dresses up as his dead victim during a masquerade, so that it would be assumed that the killing occurred much later than it actually did, and he’s seen there writing a note (in fact, a false clue pointing to another man). But the one flaw in the plan was that he is left-handed while the victim was right-handed. When one of the victim’s friends remembers it, the murderer is caught.
  • Used in the Halloween Episode of Power Rangers Dino Charge: One of the six Rangers has been replaced by an Evil Twin duplicate, and Kendall needs to figure out which one it is. She uses a lie detector, but she's ultimately able to determine the fake based on one detail: Koda is the only Ranger on First-Name Basis with her, and he had repeatedly called her "Ms. Morgan" instead.
  • In the Red Dwarf episode "Psirens", the imposter Lister can play the guitar really well; the real Lister only thinks he can. In the same episode, Imposter!Kryten calls Lister 'Dave', while the Real Kryten always calls him 'Mr. Lister'.
  • A season one episode of Sanctuary involved Magnus and Will being trapped in a crashed plane with a shapeshifting abnormal. Magnus discovers it when it's masquerading as Will when she asks for coffee instead of tea. The real Will would know that Magnus hates coffee.
  • On Scandal, the team is attending a dinner at the White House. Huck strikes up a talk with a Navy man in full uniform. However, Huck notes the medals the man is wearing are in the wrong order, a mistake a true Navy man would never make for such an important function. He tells Jake, a former Navy man himself, who agrees this is wrong. It turns out the man is a radical out to kill a visiting dignitary, the Secret Service able to stop him just before he does so.
  • In the season two premiere of Sleepy Hollow, Ichabod battles an evil Ichabod while rescuing Abbie from purgatory. The winner is about to leave purgatory with Abbie when he calls her "Lieutenant", as he always does... but he uses the American pronunciation, something the real Ichabod would never do.
  • Smallville:
    • In "Oracle", a Brainiac duplicate impersonates Jonathan Kent to have Clark kill Lionel. The problem is that, as Lionel points out, the real Jonathan would not ask Clark to kill anyone. This reveals "Jonathan's" actual persona.
    • Since Earth-2 Lionel is biologically the same person, he thinks that he can fully get away with seizing control of LuthorCorp from Earth-1 Tess. The only thing that's different between himself and his Earth-1 counterpart is that their fingerprints are opposites of each other. Earth-2 Lionel realizes this and reissues papers so that his fingerprints are on the new record, but he forgot one thing: since in his universe Tess was never given up for adoption, he overlooks the fact that all of the papers Earth-1 Lionel left at the orphanage with her have his fingerprints on them. This allows Tess to prove that he's a fraud and regain control of the company.
    • In "Harvest", Clark loses his powers and he and Lois are held prisoner in a small rural village of religious fanatics who want to sacrifice them. They attempt to escape at one point by wearing the local clothing and walking out but are caught because of Lois' nail polish.
  • Star Trek: Deep Space Nine:
    • The Changeling who'd replaced General Martok for at least several months finally gives themselves away when they tell Sisko, O'Brien, Odo, and Worf that in their attempt to kill Chancellor Gowron (believing, incorrectly, that it's Gowron who's been replaced by a Changeling) there shall be no "honor-duel". And Klingons are obsessed (usually) with honor. It's this that clues Odo in that Martok isn't who he says his is. The fact that he then attempts to murder Odo, in plain view of a dozen armed Klingons, also helps.
    • In "Inquisition", Bashir finds himself confronted by crewmates accusing him of being a traitor. In a fit of desperation, he grabs O'Brien's shoulder—and notices when he doesn't react with pain despite having recently injured said shoulder. Bashir then points out that O'Brien had dislocated the shoulder, but claims it was while playing springball; when O'Brien says only that he feels better now, Bashir reveals that it was actually a kayaking injury. At this point, O'Brien and the others disappear, revealing that Bashir is in a holo-simulation.
  • In the "Datalore" episode of Star Trek: The Next Generation, Wesley figures out that Lore is impersonating Data because Lore uses a contraction, which Data doesn't do. (In a now-infamous mistake, the real Data used a contraction in the episode's final scene and depending on who you talk to it either wasn't noticed or they didn't have time to do another take. This also launched a thousand, or at least half a dozen, wild mass guesses when it was noticed.)
    • In "The Most Toys", a collector abducts Data and makes it look like he died in a shuttle explosion. He loads the shuttlecraft with the exact right quantity of materials to mimic Data's body, but he doesn't account for a transmission that Data was meant to have sent between the time where he was abducted and the time when the shuttle explodes. Geordi knows that Data is too precise to forget the transmission or decide not to bother with it, so when he notices the discrepancy a few days after the incident, it's the first hint that something's a little bit off about the whole thing. (It takes them a little longer, and a bit more evidence, to realize exactly what's happened, but it's the first piece of the puzzle.)
  • In Stranger Things, Joyce knows the body at the morgue is not her son's because The Conspiracy missed a birthmark. Also, Hopper realizes something is wrong because, had Will actually died the way the state police said (falling at the gorge), his body would have been clearly smooshed by the impact on the water.
  • Supernatural:
    • Crowley has two of his demons shapeshifting as Sam and Dean Winchester to get information from Kevin Tran. Kevin tumbles to the ruse because the demons are too nice to him, which Crowley can only find ironic.
    • In another, sadder example of this trope, an early episode has a monster impersonating John Winchester, the boys' father. Towards the end of the plot, he hugs Dean and tells him that he loves and is proud of him for all he's which point Dean immediately destroys the beast, pointing out that the real John would never say such a thing.
  • In Travelers, the information the Travelers have on the people whose lives they're taking over is often incomplete or lacking context. The woman who becomes Marcy has learnt everything she knows about her from her Facebook page, unaware that it was just a writing exercise and that Marcy was actually severely brain-damaged, which is something that the new consciousness inhabiting the brain doesn't inherit. She blows her cover the moment she opens her mouth and has to create a new one on the spot.
  • Ultra Series
    • An episode of Ultraman 80 had a group of villainous androids posing as their peaceful creators, the Fantas Aliens, and coming to Earth to propose an alliance treaty. However, Takeshi Yamato, being Ultraman 80's human form and having knowledge of various alien races, are able to tell the peaceful aliens are actually imposters - the Fantas Aliens are mammals, just like humans, but the androids have cold, clammy skin when one of them shook hands with Takeshi.
    • Ultraman Mebius sees an Alien Babalou take on the form of Mebius's ally Ultraman Hikari clad in the Aarb Gear when attacking Earth, to make the people of Earth lose faith in Ultramen. However, Mirai Hibino, the human form of Mebius, immediately figures out that it's not really Hikari because Babalou's disguise included the Knight Brace, which Hikari had previously given to Mebius before he left Earth.
  • The Wild Wild West's "The Night of the Colonel's Ghost" has Artie impersonating Ulysses S. Grant in a bid to flush out a not-as-deceased-as-previously-thought colonel who's looking for hidden gold. Artie-as-Grant lists the battles the colonel and Grant fought in and all goes well - until he mentions a battle that took place after the colonel faked his demise.
  • The Lifetime movie The Wrong Prince Charming has Anna falling for the handsome Prince Edward of Devonshire, in Los Angeles for business. She soon agrees to a deal giving him $200,000. But her friend is suspicious, noting that during a talk of driving in his home country, Edward used miles per hour rather than kilometers. When her friend vanishes, Anna finds an e-mail from her of a news story of the Prince attending a factory opening in Devonshire...which is on the same day he was with Anna in California. Anna realizes she's fallen for a dangerous lookalike con man.
  • Young Blades episode "The Chameleon", the title assassin is able to "bend light" to make himself look like anyone. He does so for musketeer Jacques...unaware that "Jacques" is actually Jacqueline, a woman disguised as a man to join the Musketeers. D'Artagnan (who knows her secret) is quickly able to see through the act as "Jacques" is acting like a true man, rather than a woman pretending to be a man.

    Myths & Religion 
  • The traditional Japanese greeting "moshi-moshi" is a version of this. Shapeshifting youkai wouldn't be able to pronounce it right, giving themselves away.
  • The Bible: In Genesis chapter 27, Jacob disguises himself as Esau by wearing Esau's clothes and having furry goatskins on the back of his hands and the back of his neck so that he could get the firstborn blessing from his father Isaac when he was near death. Because Isaac was blind at that point, the impersonation works except for one detail that Isaac noticed (although strangely it doesn't stop Isaac from going ahead with the blessing): Jacob didn't bother to disguise his voice, so Isaac recognized his voice as that of Jacob.


    Video Games 
  • Arknights: In Episode 10, the Damazti Cluster disguised themselves as a member of the La Résistance to infiltrate the group for the purpose of luring them into a trap. They eventually got discovered due to not knowing or remembering that the man they disguised themselves as adored metal crab toys, dismissing one that was found to give to the man as "worthless".
  • In most Hitman games, Agent 47 can disguise himself as an employee/guard to help him get in restricted zones. However, despite his amazing ability to blend in, the detail he can't duplicate is their behavior, leading him to get caught if he lingers. Any time 47 has to interact with his targets in disguise, due to his "upbringing", he barely knows how society functions and gives off a creepy vibe - the one exception is disguising as a Catholic priest, since he actually has trained to enter the clergy.
  • In Saints Row: The Third, The Boss attempts to impersonate Cyrus, the leader of STAG, but fails to act appropriately in any way. Given how poor the act is, it takes The Boss a surprisingly long time to get caught.
  • During chapter 12 in Mafia II Henry convinces Vito and Joe to get into the "dope" business, and later in the mission when the trio leave the warehouse after getting their drugs, they get approached by several alleged police officers, Joe notices that the "officers" aren't wearing proper shoes that fit their uniforms, which causes a shootout to happen.
  • Team Fortress 2:
    • For a period of time in between major updates, Spies suffered from one glaring flaw in their disguises- lack of unlockable weaponry. A Spy's disguise would always show the stock loadout for the class, even as reskins and alternate weapons became widely available and popular, so if you had one player on your team without unlockables, you could be almost certain that they were a spy. This was later patched out, and now Spies imitate the chosen weaponry of their disguise target.
    • Another common sign of a poor spy is always having their primary out no matter the context. For example, real Medics will almost always have their medigun out for emergency healing, so a Medic with a syringe gun out is very suspicious.note 
    • Besides the above, there was one glaringly obvious tell once attached to the Medic disguise that made it completely unusable at the game's launch: When looking at a Spy-disguised-as-Medic, the "Ubercharge Built" meter didn't show up in their namebox like it would for a real Medic. The meter now shows properly, but permanently shows 0% for disguised Spies, which is only marginally less suspicious - every half-decent Medic outside of spawn has some charge built up.
    • Spies cannot imitate class-specific movement, like a Scout's double-jump and the Soldier and Demoman's rocket jumping. They're also slower than Scouts and faster than Heavies.
  • In Magia Record: Puella Magi Madoka Magica Side Story, Rena's magical girl abilities involve her being able to imitate other magical girls and take on their appearance. But her imitations are always influenced by her perception of the person, so even if she can get many things down right, minor parts always let others recognize her as Rena merely imitating them quickly. When she transforms herself into Momoko, Kaede recognizes her instantly because Momoko's stance is different.
    • In the anime of the game, Rena's imitations always have her natural blue-colored eyes, even when transformed. And in Episode 2, she transforms into a grayhaired magical girl to not be noticed by Kaede and Iroha, but Kaede recognizes her because she still had the rabbit mascot that Rena and Kaede share hanging on her bag.
  • At one point in Bayonetta, the title character has to save Cereza from a giant Beloved angel. When the angel dies, Cereza falls into Bayonetta's arms... or, rather, the arms of a Joy angel mimicking her. The only giveaway? Angels can't hide their halos. A second giveaway is the fact that the Joy is fully-clothed, despite Bayonetta being in the middle of a demon summoning at the time.
  • In order to get into the black market in Ueno in Shin Megami Tensei IV, you have to say "Erewan" (in fact, the player has to type it into the game). Presumably this is a shibboleth designed to root out demonic infiltrators.
  • Your clone in the Citadel DLC for Mass Effect 3 has more sort of forgotten every detail beyond "has the Normandy" and "wears an N7 badge"; doesn't have the charisma, doesn't have the flexibility, doesn't have the compassion, doesn't have the cybernetics, doesn't have a clue. You can actually point out, during the final confrontation, that there is no way the impostor is going to be able to fool, say, Admiral Hackett for even a minute. The impostor did, to their credit, remember that despite being a clone they would need to replace the original's recorded fingerprints with their own, and arranged a complex scheme to do just that.
  • Star Trek Online: The side mission "Standoff" has the True Way try to frame a loyal Cardassian Self Defense Force gul as a traitor to Cardassia. The video that makes up part of the incriminating evidence turns out to actually be of a changeling in Gul Antos' shape, but the changeling got Antos' dominant hand wrong.
  • In Banjo-Tooie, Mingy Jongo refers to Banjo by name (as opposed to Mumbo referring to him as Bear).
  • In the Dark Souls trilogy: Mimics can be told apart from real treasure chests by looking for a single small imperfection in the disguise. In 1 and 3, the chain hanging off the right side of the chest will curve backwards on real chests and forwards on Mimics; while in 2, real chests do not have visible locks on them, but Mimics do (which is really quite stupid on their part, since most people probably won't bother trying to open chests they think are locked). There's also a second tell: If you watch them for long enough, mimics breathe.
  • In BlazBlue: Central Fiction, Phantom attempts to manipulate several characters during Act 1 by creating illusory versions of other characters. However, Jin sees through a false Ragna because he was unusually calm, and Rachel spots another one because he was too polite to her. Tsubaki also notices that a fake Kagura is being strangely formal.
  • Fate/Grand Order:
    • Sherlock Holmes impersonates Edmond Dantes at one point. He gives himself away almost immediately because he introduces himself as Edmond Dantes, but the real Edmond always calls himself The Count of Monte Cristo or The Cavern King.
    • In the same chapter, Yan Qing impersonates Cursed Arm Hassan to gain the party's trust because, in the entire game's storylines, Cursed Arm Hassan is one of the most stalwart allies of Chaldea. The protagonist then has the option to notice his disguise after Moriarty baits him by giving him the choices of whiskey, low malt, and malted beer drinks and he chooses whiskey. Cursed Arm Hassan is a Muslim and a leader of a religious sect and thus forbidden to drink alcohol.
  • Professor Layton:
    • In Professor Layton and the Curious Village, Layton's self-proclaimed rival and Master of Disguise Don Paolo impersonates Inspector Chelmey, whom none of the characters even know...but Layton reads an article about the real Chelmey, which states as an amusing fact that he is crazy about his wife's pastries. Cue Don Paolo as Chelmey throwing a fit at the butler for bringing him sweets, which he apparently abhors.
    • Poor Don Paolo often falls victim to this. In Professor Layton and the Diabolical Box, his disguise as Flora, the Professor's ward, is uncovered when "she", upon seeing a photograph of the titular box, comments that the pattern on the top looks like a goat. This was supposedly Flora's first time seeing this box...but by that point, an accident had caused a piece of the photograph to become lost, making it look more like a frog. Only someone who'd seen the real box before the accident—namely, Don Paolo—could have recognized what the animal was supposed to be.
    • Professor Layton and the Unwound Future:
      • Don Paolo makes yet another mistake when he's impersonating Dr. Andrew Schrader. When the Professor and Luke visit him in the future, he expresses surprise at seeing both his old friend and "little Luke" again, despite the fact that the Luke Triton of the future is a tall young man. Since Don Paolo had only encountered Luke as a kid in previous adventures, this tips Layton off to the fact that "Schrader" is actually the former.
      • Later in the game, Layton and Luke meet up with Dean Delmona, head of the professor's university, in the future. As they chat, Luke notices some bottles of pomade in the room where the dean is staying, and Layton notices that his hair has gone white. When Layton later outs the "dean" as his rival Don Paolo in a nearly-perfect disguise, he reveals that his hair gave the trick away—Delmona is already bald in the professor's original time period, so he wouldn't have needed any hair product, nor would his toupee turn grey with age since it's fake. Don Paolo only uses the pomade to keep his infamous mustache looking sharp.
  • At one point in Metal Gear Solid 3: Snake Eater, you have to infiltrate Groznyj Grad disguised as a local General named Raikov (who looks suspiciously like Raiden from MGS2) and to Snake's credit, once you knock him out, steal his clothing, and wear a latex mask of his face, no one is any the wiser. Where it falls apart is when he encounters Volgin, aka Raikov's lover, who greets him by grabbing his crotch and almost immediately figuring it out, though to be fair, there's no way Snake would've known that. In addition, when you're disguised as a soldier, you'll be found out if you neglect to salute other soldiers who do the same to you.
  • Near the end of Minion Quest: The Search for Bowser, "Bowser" tells Captain Goomba to destroy Mario, who is on his way to Bowser's Castle. Goomba seems confused about it at first (since Bowser would never say such a thing), but agrees anyway. Sure enough, "Bowser" is Cackletta possessing Bowser as Bowletta on a plan of Fawful in hopes the Koopa Troop and the Mario Brothers would destroy each other, though Lakitu overhears their conversation and informs Captains Goomba, Shy Guy, Boo, and Koopa Troopa.
  • In Vampire: The Masquerade - Bloodlines, the player character is sent to go check on the Malkavian Primogen so that they can serve as an apolitical witness to Nines Rodriguez (who is actually Voluntary Shapeshifter Ming Xiao pretending to be him) fleeing the scene of the Primogen's murder. One problem: while she's able to recreate his appearance and voice convincingly, Xiao fails at replicating his mannerisms and inflections. She even accidentally slips back into her own elegant and polite speech pattern near the end of your short interaction, which is a distracting far-cry from Nines' usual gruff-but-casual demeanour. Even your character, a naive fledgling vampire who met Nines mere days prior, could tell something was off.
  • Final Fantasy XIV has Ardbert seemingly back from the dead during the "Echoes of a Fallen Star" story in Shadowbringers. Naturally, the player character and their Scion companions aren't buying it. When confronted, the player can choose to ask the imposter how Seto is doing. The man says that he will dearly miss him. Except it's completely false since Seto is alive and well (and very long-lived), something that the actual Ardbert would know. The imposter doesn't bother trying to lie any further and reveals himself to be Elidibus.
  • Do You Copy? has an example that's crucial to beating the game. The spotlight is incredibly bright, and if you turn them on the first time around, the hiker responds in a way that implies he knows how to get to Tower 4, and doesn't need guidance beyond that (though he sure as hell needs reassurance). The fact that the 'hiker' is asking for directions despite already knowing how to get to Tower 4 is a dead giveaway that it's really the Goatman speaking.

    Web Comics 
  • When Destania from Dan and Mab's Furry Adventures pretends to be Biggs to send her son Dan on a wild goose chase, she gets the hairstyle wrong on purpose to leave a subtle clue purely for sport.
  • In The Dragon Doctors, "Elizabeth", the leader of a gang of thieves, disguises herself as Goro with a specialized identity theft spell that hides her previous forms. Unfortunately for Elizabeth, Sarin instantly noticed that she couldn't see Goro's old male form.
  • In El Goonish Shive, Grace and Ellen play a game of Spot the Imposter with Tedd but he quickly guesses who's who because there was no "Grace" form at that time and Ellen doesn't act like Grace.
  • In In Our Shadow a lab rat tries and bait a raccoon squadron into a trap by pretending to be a wounded raccoon officer herself, using her telepathic enhancements to get details like the squadron name and rank of a legitimate sergeant right. However, the raccoon colonel sees through it immediately because she claims to have escaped a situation that would definitely have been fatal, her offhand reference to a raccoon sport using an outdated name and that the sergeant she claimed to be doesn't know him well enough to be able to recognise him by his voice through a megaphone.
  • Parodied in Oglaf with the slutty master of disguise, whose otherwise flawless attempts at impersonation are always marred by his insistence on dressing as a slutty version of the person he's impersonating and claiming that he "won't sell out" when asked about it.
  • Planet of Hats: How Spock is able to tell between Kirk and a man doing a good imitation of him. Only the real Kirk would unnecessarily rip his shirt in a fight.
  • In Rusty and Co., the derro make a bunch of impostors of Stabs. Every single one of them, bar none, got something wrong — in some cases, dramatically so. The first one Presti runs into was pretty subtle (she was just missing the hair on her halfling feet), but Presti caught her out by asking about the makeshift bazooka she'd last left with the real Stabs; the impostor said it was too heavy to lug around (while the real Stabs would know it was enchanted to weigh very little).
  • In Sam & Fuzzy, the only clue that the mole in Sam's reconstructed Ninja Mafia is the shapeshifting Jess masquerading as Mr. X is that when she's transformed, X's missing arm is on the wrong side of his body.
  • Changelings in Star Mares are bad at colors. The Nightsisters in particular have a problem getting the eyes right.
  • In Season 16 of Survivor: Fan Characters, one of the things that tips off the characters to the "Bonnie" who was voted out actually being an actress hired by the real (disguised) Bonnie to impersonate her is one of them recalling that he didn't see any tattoos on "Bonnie"'s back while she was swimming.

    Web Original 
  • The Noedolekcin Archives: In "Nick Jr. Anomaly (2001, Found Footage)", the 1993 Nick Jr. "Father and Son" logo plays during the credits to an episode of Little Bear, but the writing on Nick's chest is rendered backwards. This is the first hint that this "Nick" is actually Kirk Odd in disguise.
  • In this short by CocobrED, Kaepernick catches out a demon impersonating a Jehovah's Witness by his wearing of a cross (which real Jehovah's Witnesses do not wear because of their beliefs regarding idolatry).

    Western Animation 
  • In the Adventures of Sonic the Hedgehog episode "Tails' New Home", Sonic and Tails believe that they found the latter's parents and the former returns him to them. However, Sonic starts reminiscing about their first meeting and realizes he's been had - they kept calling him "Tails", not "Miles", his real name. Tails' "parents" were robots and he was captured by Robotnik.
  • Arabian Knights: In "The Spy", Zazum is accidentally separated from the Knights during a confrontation with Bakar's guards. A shapeshifter in Bakar's army transforms into Zazum so as to infiltrate the Knights' home base. Unfortunately, he didn't learn the habits of "the real beast": when offered hay and an apple, he refuses both. Furthermore, when his tail is pulled, he doesn't bray and go into his tornado spin. Nida doesn't have this issue when she impersonates the changeling.
  • The Batman: In the episode "Clayfaces", the Joker and his two henchmen Punch and Judy are at a dog food factory, where Joker is putting his Joker toxin into the dog food so that the dogs will laugh like hyenas. Judy comments that this plan "stinks on ice" and Punch agrees. Joker tells them to never ever talk to him like that, then follows up by noting that they've never talked at all before this point. It's Clayface impersonating them in another attempt to get revenge on Joker.
  • Batman: The Brave and the Bold: In "The Mask of Matches Malone", Two-Face impersonates Batman at one point, but gives himself away almost immediately by using guns, when Batman Doesn't Like Guns. When this is pointed out, Two-Face says he didn't forget, it's just that he cared more about winning than accuracy.
  • When master of disguise Anyface exposes himself as an impostor of Paul McCartney in The Beatles episode "No Reply" as a bevy of fangirls chase him, Ringo points out "A Beatle would have known enough to run!"
  • Codename: Kids Next Door:
    • One episode, when Numbuh One is trapped in a Lotus-Eater Machine, he realizes what's going on during a pool party, when he points out that Numbuh Four can't swim.
    • In the episode "P.O.O.L.", Numbuh Four's friends are all replaced by evil twins from a negative universe originating from the pool. Hilariously, Numbuh Four fails entirely to spot that Numbuh One and Lizzie are fakes despite them acting very much like villains... but when he discovers that Numbuh Three has mean-looking eyes, that clues him in that his friends must be evil twins from another universe because Numbuh Three would never look like that. Numbuh Four calls this deduction "being a friend".
  • In one episode of Cyberchase, Digit attempts to impersonate (the) Hacker using an obviously robotic suit that completely fools his henchmen. Unfortunately, the real Hacker is able to call out the fake for being so perfectly symmetrical, the heroes forgot to include his pocket protector.
  • Dexter's Laboratory: In "The Muffin King", Mom makes a batch of her famous muffins and then heads to the store, warning Dexter and Dee Dee to keep the pastries safe—they're Dad's Trademark Favorite Food, and he'll stop at nothing to eat them before dinner. At one point, Dad dons the Paper-Thin Disguise of Mom's clothes and tells the kids that they're going to Chubby Cheese's for dinner instead, giving him time to try to take the muffins...only for Dexter and Dee Dee to come back and expose him, because they realized that Mom was "looking a little stubbly"—Dad forgot to shave before disguising himself.
  • Zigzagged in one episode of Ed, Edd n Eddy (it happens, but the imposter still fools the victim). At the end of an episode, Sarah and Jimmy use a two-person costume to dress up like Eddy's brother in order to scare him, and then tell him to get them ice cream. Eddy is at first a little suspicious because his brother is lactose intolerant, but Sarah's acting is so convincing that he's scared into complying. Eddy's reaction is, of course, a Foreshadowing to the movie, where it's discovered how much he really is terrified of his brother.
  • Extreme Ghostbusters: In the episode "The Ghostmakers", the demon possessing Eduardo’s body eats sandwiches with mayonnaise in them (which the real Eduardo hates). The demon possessing Garrett’s body, however, takes the cake by doing something a paraplegic person can’t do: stand on his own two feet. The latter signals to the rest of the team that something's gone very, very wrong.
  • Gargoyles uses this for drama on various occasions;
    • In "Shadows of the Past", Goliath is attacked by the spirits of the Captain of the Guard and Viking chief Hakon, the two men responsible for the deaths of the original Wyvern Clan. When the two spirits attack Goliath by animating stone to create the illusion that he is being confronted by the spirits of those slaughtered gargoyles, Goliath initially cannot fight back out of his own guilt. However, he realises that these gargoyle "ghosts" are fake when Demona is part of the attack, as Goliath knows that she never died.
    • In another episode, Goliath is captured by an evil shapeshifter, and when Elisa and her allies go to rescue him, the creature assumes her form, forcing the heroes into a Spot the Impostor scenario. Goliath then calls out a question — "Elisa, tell me truth! Was there ever a time, even for a moment, that you doubted me?" One Elisa promptly responds "Never!" — and that's the one Goliath names as the fake. The monster couldn't have known that Elisa and Goliath's relationship is brimming with doubt, especially since he was responsible for the rift between them at the start of the episode.
  • Jackie Chan Adventures: In "Attack Of The J-Clones", Jade is able to spot Paco as a magical clone because he pronounces her name correctly, unlike the real Paco, who always pronounced it "Yade." Truth in Television. There is no equivalent to the English "J" sound in the Spanish alphabet (their "J" sounds like an English "H", e.g. "jalepeño"), so many Spanish-speakers even those who are basically bilingual still talk about watching "Yaws" or "Yudge Yudy".
  • Johnny Test: In the episode "Johnny Johnny", Dukey has to figure out which of two Johnnys is a robot. When they answer his first two questions perfectly, he asks a math question. One Johnny answers immediately, and Dukey blasts him. The reason being the real Johnny has to use his fingers when he's asked such a question.
  • Clayface does it again in an episode of Justice League while impersonating The Flash. He tries to bluff Batman into thinking he (Flash) had taken down Sinestro, who is only pretending to be unconscious. Batman immediately throws an explosive batarang at him. Turns out Clayface had overdone the slang.
    Batman: You overplayed your part, yo.
  • Kuu Kuu Harajuku: When the Kimberlys use a stolen holographic generator to swap appearances with HJ5, the Kimberly disguised as Music surprises Rudie when she is genuinely nice to him. This causes Rudie to realise what happened because the real Music is always being snarky to him.
  • League of Super Evil: In "Voltar Squared" (continuing from "Dial E for Evil") Humungo dons Voltar’s outfit so he can manipulate the rest of L.O.S.E into helping him conquer the earth. While he succeeds in fooling them despite his radically different body shape other than sharing the same height, he blows his cover by thanking Red, Frogg, and Doomageddon for their hard work, which as Red points out is something that the real Voltar would never do.
  • My Little Pony: Friendship Is Magic:
    • It's the principal failing of the Changelings, as "getting into character" isn't their strongest suit. More specifically, fake Cadance doesn't recognize the rhyme that she and Twilight used to sing. This is the first clue Twilight gets that something is wrong. In the IDW comics, a Changeling mimicking Derpy Hooves forgets to do the Fish Eyes. Another one has to smack it to make the eyes cock correctly.
    • In the episode "Too Many Pinkie Pies", in order to separate the real Pinkie Pie from her army of duplicates, Twilight Sparkle and friends round them up and make them watch paint dry. Any one of them that gets distracted is destroyed — the real Pinkie Pie is the only one willing to watch something so boring for so long since she would rather be with her friends in the future than have fun now.
    • The episode "Spike at Your Service" features Spike doing favors for Applejack because she saved his life from Timberwolves. The girls decide to stage a fake Timberwolf attack so that Spike can "save" Applejack from doom. This didn't work because they forgot the bad breath that they have. Then, real Timberwolves show up and Spike ends up having to save Applejack for real.
    • Hilariously subverted in "Dragon Quest." When Spike joins the Great Dragon Migration, Twilight, Rainbow Dash, and Rarity follow him in an extremely transparent dragon disguise. Since Rarity designed the outfit, it's naturally Gem-Encrusted and sparkly, which would ordinarily out it as a fake among the solid-colored dragons...but by some amazing coincidence, there's a real dragon named Crackle who looks identical to the costume, so nobody thinks it's suspicious.
  • The New Scooby-Doo and Scrappy-Doo Show: At the end of "Scooby's Gold Medal Gambit," Daphne is able to realize that the "Chairman Lewis" during the Olympic ceremonies is really Master of Disguise the Chameleon in a Latex Perfection mask, because the real Chairman Lewis can't read without his reading glasses, and the fake Chairman was reading from a document just fine without glasses.
  • In the Grand Finale of The Owl House, Amity quotes Azura by furiously challenges Luz to a witch's battle. Luz immediately notes that the real quote is a witch's duel, and Amity would never truly misquote Azura. Thus, Luz realizes her friends haven't turned against her, and are simply Brainwashed and Crazy.
  • Pinky and the Brain: When Brain decides to take over the world by impersonating Abraham Lincoln, he's not worried that people will notice that he doesn't sound like the real Lincoln because he died before voice recording devices were invented and Brain doesn't believe there's any living person old enough to have heard him talk. The oldest living American proves him wrong about the last part.
  • Punky Brewster tussles with an obnoxious clone of her that Glomer created from a photograph (episode "Double Your Punky"). What gives the clone away is that she doesn't leave a scent and the good Punky does, which her dog Brandon recognizes.
  • A Pup Named Scooby-Doo, In "Now Museum, Now You Don't," the Villain of the Week is a samurai ghost trying to swipe some swords from a museum display. When the ghost first attacks, Velma says "Kono katana wa nisemono desu"; he ignores her and takes the swords anyway. Velma then reveals the English translation—"Those swords are fake"—and comments that it's proof that someone is pulling a "Scooby-Doo" Hoax: if the ghost is really an ancient Japanese samurai, presumably he would know Japanese.
  • "Ghost World," an episode of The Real Ghostbusters, sees the entire team except Egon being captured and possessed by ghosts. Egon, sensing something is wrong, asks Janine how her sister is doing; when she responds positively, he immediately goes for his ghost-hunting equipment, as Janine doesn't have a sister.
  • The Simpsons: In "Krusty Gets Busted", with Sideshow Bob's eagerness to frame Krusty and send him to jail forever, he forgets a number of key facts that he knew about his co-star: He knew Krusty was illiterate, yet he is seen (via the security camera) reading a magazine at the counter, waiting for the store to clear out, and Bob (as Krusty) stood near a microwave oven, which Krusty can't do because he has an artificial pacemaker implanted in his heart (which was also captured via security camera). Naturally, when Bart points this out, Bob tries to bluff an explanation that Krusty was never very smart and liked to look at the pictures, but it sets up Bob's downfall. The final giveaway was Bob's foot size. Krusty has regular-sized feet and just wears the huge clown shoes as a costume, while Bob's feet actually are that big. In the robbery footage, Homer accidentally steps on the toe of "Krusty's" shoe and he yells out in pain.
  • In Spider-Man: The Animated Series Spider-Man is able to figure out that Nick Fury is actually the Chameleon in disguise after realizing he has his eyepatch over the wrong eye. (The Chameleon had gotten the disguise by looking at Fury's picture in The Daily Bugle, where a negative had not yet been flipped.)
  • On Star Wars: Detours, the Decoys are supposed to look identical to Princess Leia in every way, but they're missing her most defining feature.
  • Static Shock: In "Duped", the shape-shifting criminal Replikon kidnaps A.J. McLean and steals his identity. Virgil and his friends eventually realize something is wrong because A.J.'s tattoos were on the opposite arms.
  • Transformers: Prime:
    • In one episode, Bulkhead manages to spot a fake Wheeljack by tricking him into telling a war story about their time together in one battle. Bulkhead confirms the story is true, but the imposter forgot one detail: Bulk was actually with Optimus during the battle in question.
    • Another episode where Optimus Prime is duplicated by M.E.C.H. and controlled by a human operator, Bumblebee speaks in machine code to the imitation Optimus, only to hear in response "I'm sorry, I don't understand". Since any native Cybertronian would have understood him instantly, Bumblebee's next action is to activate his guns and fires several salvos at the imposter.
  • Total Drama: In "The Bold and the Booty-ful", Mal, who is impersonating Mike, tries to trick Zoey by saying he's the same Mike who gave her a bracelet last season. As Zoey says in the confessional, Mike gave her a necklace.
  • World of Quest: The episode "In Search of the Royal Family" has Deceit capturing Anna and disguising herself as her to lead the heroes into a trap involving finding Nestor's parents (who are actually the Catastrophe Brothers in disguise). While the trap works in the end and causes Nestor to briefly call off the quest, the others eventually figure out "Anna" is an impostor upon noting the various inconsistencies in her behavior throughout the episode, such as not understanding Way's riddles and disagreeing with her directions (the latter of which being something the real Anna never does as Quest points out) and having a completely different smell than usual according to Graer. After the fake king and queen are also exposed, Nestor mentions that he started to suspect something was off with his "parents" after they invited him to play tennis with them when he knows that they actually hate it.
  • Winx Club: In "Date with Disaster", the first hint is "Stella's" strange behaviour while looking for her ring. In addition to that, Bloom is able to tell that it's actually Darcy in disguise as she uses magic, despite Stella (at her current fairy level, at least) not being able to use magic without her ring.
  • X-Men: Evolution: In "Blind Alley", Mystique attempts to ambush Scott Summers by shapeshifting into Jean Grey. She gives herself away when she mentions the team used Cerebro to lead her directly to him. Cerebro only gives a general direction of where a mutant is in a city's worth of space.

    Real Life 
  • Older Than Feudalism: Shibboleths originate from biblical times and have been used throughout history to detect impostors (or people on the genocide list).
    • For example: the words "brânză" and "cârpă" were often used to distinguish native Romanian speakers from native Hungarian speakers. In both words the "â" is pronounced as a close central unrounded vowel, while the "ă" is a schwa. Neither of these vowels exists in Hungarian, and many Hungarian speakers tend to confuse them.
    • In German, the letters "sch" tend to be pronounced as "shhh", while in Dutch, they make the consonant cluster "/sx" instead, which is not a sound native to German. Many a Dutch WWII resistance fighter used the word "Scheveningen", the name of a Dutch coastal town, to weed out German impostors.
    • During World War 1, a British officer tried to fool an Askari of the German Schutztruppe in East Africa at night by giving him an order in Swahili. He got shot dead immediately because he could not disguise his British accent, specifically by the way English turns many long vowels into diphthongs.
    • During World War 2, the forces of the Ustasha regime in Croatia were able to detect young Serbs (who belong to the Orthodox church) by telling them to make the sign of the cross. note 
    • During the Battle of the Bulge, Germans in U.S. uniforms infiltrated the allied lines. One of the quick ways to check out an unknown soldier was to ask him to say "squirrel".
    • A similar test to spot Japanese saboteurs without coming close enough for a gander of their face was ordering them to say "Lollapalooza".
    • One famous test for German spies infiltrating American camps during World War II was asking the name of Mickey Mouse's girlfriend (Minnie, of course!).
    • Another WWII example provided a surprise inversion of the trope. Americans testing for infiltrators would say the phrase "The terror of flight". Anyone who responded "The gloom of the grave" was immediately outed as a spy. Those lines come from the third verse of "The Star-Spangled Banner", the national anthem of the United States. American higher-ups realized that German spies would practice their false identities by memorizing the entire anthem. This is an example of being too prepared, as very few Americans would know the whole song by heart; when the national anthem is sung, it's almost always just the first verse. Many Americans don't even realize that "The Star-Spangled Banner" has multiple verses to begin with. So in this case, the impostors remembered too many details.
    • The Parsley Massacre of 1937 was a period of anti-Haitian genocide carried out by Rafael Trujillo, who was the dictator of the Dominican Republic at the time. Trujillo's soldiers captured thousands of people and made them say the word perejil (Spanish for "parsley"). Those who couldn't pronounce the word the Spanish way as opposed to the Haitian/French way were deemed to be Haitians and killed.
  • During World War II, any attempt by the Germans to pass forged documents to the Soviets ended up being exposed. The fakes were recognized even by ordinary soldiers. After a long time, it became a well-known secret. Paper clips in the Soviet Union were made of ordinary steel (and in wartime, they rusted), and German paper clips (including the forgery of Soviet documents) used chrome-plated steel, which doesn't rust.


Video Example(s):

Alternative Title(s): Impostor Forgot One Detail, Impostor Jamie Has No Accent


Lucifer's Honor

While Michael got the "sex maniac" part down, he playing his cards wrong by trying to do it while in a relationship with Chloe, knowing that the real Lucifer was more honorable than that.

How well does it match the trope?

5 (12 votes)

Example of:

Main / ImposterForgotOneDetail

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