->''"Your shuriken pouch is on your left leg, but Naruto is right handed."''
-->-- '''[[Manga/{{Naruto}} Sasuke Uchiha]]''' telling it like it is

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. Subtrope of SpotTheImpostor.

Compare to SomethingOnlyTheyWouldSay and BluffTheImpostor. One result, and often the dead giveaway, of an ImpostorExposingTest.

See also CoverIdentityAnomaly and SpottingTheThread.

'''Expect spoilers!'''


[[folder:Anime and Manga]]
* In ''Anime/MagicalGirlLyricalNanohaAs'', when the masked men take on Nanoha and Fate’s identities, parts of their Barrier Jackets are not the correct color. This is likely because [[spoiler:cats, and - by extension - {{Cat Girl}}s, are [[ColorBlindConfusion colorblind]]]]. Not that it really matters, since the person they were trying to fool had never seen Nanoha or Fate in their Barrier Jackets.
* In ''Manga/FullmetalAlchemist'', Hughes is able to realize that Maria Ross is being impersonated by Envy because she doesn’t have her [[BeautyMark mole]]. [[spoiler:This doesn’t save him from being killed, nor does it save Ross from being framed for his murder in the manga]].
* ''Manga/{{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 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 IdiotHero who could ''never'' have gotten the password correct on his first try ([[KansasCityShuffle this being Sasuke's plan with the password all along]]).
** 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 ''Manga/{{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 ''Manga/TsubasaReservoirChronicle'', 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-[[UsefulNotes/JapaneseHonorifics kun]]". They're not in first name basis anymore; their past together has been written out of her memories as per the deal he made with Yuuko.
* In ''Manga/DetectiveConan'', there is a flashback episode where a grown up Shinichi is combating [[PhantomThief Kaito Kid]] (who can near perfectly disguise himself as anyone). Shinichi figures out which police officer Kaito was disguised as because [[spoiler:he was the only one who remembered his own I.D. number. ''No one remembers their I.D. number''.]]
** A currently manga-only story (as the anime hasn't caught up to it yet) 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; 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).
* In ''Manga/{{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.
* ''Anime/MarineBoy'': 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 ''Anime/DragonBallZ'', 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 17 and 18 despise the man.
* In a story of ''Manga/ToLoveRu'', 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 [[ACupAngst Nana]] into beating him to a pulp.
* In the first ''Anime/SailorMoon'' 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.

* The ''Franchise/SpiderMan'' mini-series ''Spider-Man: Hobgoblin Lives!'', 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 Formura get a HealingFactor and have recovered from seemingly deadly injuries,
* Prior to ComicBook/TheCloneSaga, the Chameleon used synthetic androids disguised as his parents to discover Peter's relation to Spider-Man; these duplicates were almost perfect in appearance, personality, and almost memory, so much that Peter's Spider-Sense didn't go off until their suppressed programming did. The one missed detail occurred when they offered to take his Aunt May to Uncle Ben's grave on their anniversary. May had actually married Ben in a private ceremony a month before the formal one, and the only witnesses other than the priest were Richard and Mary Parker, Peter's parents; because the two androids didn't know May's anniversary - something that could not have been programmed into their memory by the Chameleon nor anyone else - May suspected something was wrong, and this eventually led to the ruse being discovered.
* In ''ComicBook/TheSmurfs'' comic book story "The Fake Smurf", Gargamel (and Hogatha in the AnimatedAdaptation) 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 ended up falling off, and Gargamel was soon spotted and revealed to be the fake Smurf.
* Early in ''ComicBook/TheSuperiorFoesOfSpiderMan'', Boomerang figures out that [[TheMafia the gangster Hammerhead]] menacing him is actually a disguised [[MasterOfDisguise 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.
* This is what pings Comicbook/LoisLane into realizing the Cyborg Superman isn't the real Franchise/{{Superman}} in the "Reign Of The Supermen" arc of ''ComicBook/TheDeathOfSuperman'' - he casually mentions to Comicbook/{{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).
* ''ComicBook/PaperinikNewAdventures''
** During one of the many attempts of the Evronians to capture [[PhysicalGoddess Xadhoom]]: after identifying her as a Xerbian, they lure her on 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... [[{{Troll}} 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 [[{{Ruritania}} 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 [[ArrangedMarriage 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 [[BigDamnHeroes they show up for the rescue at the decisive moment]].
* ''Comicbook/LaffALympics'': In "The Day the Rottens Won", Dynomutt figures out there's an imposter pretending to be Blue Falcon when he asks why Radley Crown didn't show up for the opening ceremony and the imposter, not knowing Crown is the real Blue Falcon, asks how he should know.
* Used in a {{Retcon}} StoryArc in the Comicbook/FantasticFour. In 1984, 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 in 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.
* ''ComicBook/{{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? [[spoiler:That's what helps Medusa realise it's Maximus in disguise.]]

* In the Fresno, [[UsefulNotes/{{California}} California-based]] Doctor Who Audio Dramas' continuity, the [[Creator/TomBaker David]] [[{{Expy}} Segal]] [[TheNthDoctor 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 ''Fanfic/WhiteDevilOfTheMoon'', the impostor, posing as Reinforce, referred to Hayate and Signum as 'the two of them' [[spoiler: when the real Reinforce would have noticed that Signum was in Unison form, indicating the presence of a third person.]]
* In the ''Fanfic/PonyPOVSeries'', 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. [[spoiler: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 ''FanFic/OjamajoDoremiRiseOfTheShadows'', 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 [[CastsNoShadow do not cast shadows of their own]]. That, and she noticed something "off" about "Majorin's" behavior.
* In ''Fanfic/WakingNightmares'', 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 [[NoodleIncident some unspecified incident]]) and lead the imposters into an ambush.
* In the original ''Fanfic/{{Shadowchasers}}'', 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 ''Film/ANewHope'', she notices that the Darth Vader statue has a ''green'' lightsaber, and realizes ''that'' must be him.
* In ''[[https://www.fanfiction.net/s/3482033/1/Shadow-Realm-PI 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 [[DoesNotLikeShoes go barefoot]].
* In ''[[https://www.fanfiction.net/s/9723228/1/Fly-Me-To-the-Moon-A-Buffy-Bayonetta-tale 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 ''Fanfic/EquestriaGirlsFriendshipSouls'', 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 [[TheNoseKnows her scent is wrong]].

[[folder:Films -- Animated]]
* Subverted in ''WesternAnimation/ToyStory3''. 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 [[TheDandy Ken's idiosyncrasies]].
* In ''WesternAnimation/{{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.

[[folder:Films -- Live-Action]]
* In ''Film/TheSorcerersApprentice'', 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 pretty much just confirmed the falseness of the imposter!
* In the movie ''Film/DeadAgain'', 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.
* In ''Film/HarryPotterAndTheGobletOfFire'', Barty Crouch realizes that Mad-Eye Moody is actually [[spoiler: his son]] when Moody licks his lips nervously, which is an established CharacterTic for [[spoiler: Barty Crouch Jr]]. Dumbledore figures out that this Moody is fake because [[spoiler: the real Moody would never take Harry out of Dumbledore's sight after Harry arrived back in the maze with Cedric's body.]]
* After killing the BigBad in the ''Film/TotalRecall2012'' remake, 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. This begs the question of why she didn't just kill him while he was sleeping.
* In ''Film/TheMasterOfDisguise'' 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 {{Mook}}s by pretending to be a [[Film/{{Jaws}} 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, the British spy in ''Film/InglouriousBasterds'' is given away 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.
* In ''Film/WildWildWest'', Artemis Gordon has a nearly foolproof disguise as President UsefulNotes/UlyssesSGrant (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. It doesn't help that "Grant" keeps going on and on about [[ButHeSoundsHandsome how great an agent Gordon is.]]
* ''Film/JamesBond'':
** In ''Film/FromRussiaWithLove'', 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 ''Film/{{Thunderball}}'', Colonel Jacques Bouvar DisguisedInDrag as a rich widow. Bond spots him when he opens his car door himself instead of waiting for the chauffeur to do it.
** In ''Film/YouOnlyLiveTwice'', Bond disguises himself as an astronaut, but is spotted when he carries a piece of equipment that should always be carried by an assistant.
** In ''Film/OnHerMajestysSecretService'', James Bond impersonates Sir Hilary Bray. The bad guys expose him when he is caught in his usual antics of seducing women. Apparently, the real Bray was gay or asexual.
* The T-800 in ''Film/Terminator2JudgmentDay'' calls John Connor's foster parents, and notices that the dog is barking wildly in the background. (It's been established earlier that dogs react this way to terminators.) He asks John what the dog's name is (Max), and then mimics John's voice, asking what's wrong with "Wolfie". When John's foster mom doesn't correct him, the T-800 concludes that John's parents have been killed and impersonated.
* ''Film/TheDarkSideOfTheMoon'': 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 ''Film/TheLastJedi''. [[spoiler:When Luke sends an AstralProjection 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 - [[BatmanGambit 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.]]

* In ''Literature/MaximumRide'', the clone meant to replace Max has little knowledge of the flock, which means she doesn't know that Iggy is the TeamChef despite being blind, while she is supposed to be [[LethalChef a terrible cook]]. [[spoiler: Her cover is blown by the fact that six-year-old Angel is a ''[[{{Telepathy}} mind reader]]'', and was never fooled in the first place]].
* This is the FatalFlaw of the main antagonist of ''Literature/NeedfulThings''. He cooks up fake evidences 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.
* ''Literature/ASongOfIceAndFire''
** 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. [[spoiler:Arya Stark is told off every time she gives herself away with the {{Character Tic|s}} 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 Creator/AllenSteele'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 [[YouNeverAsked they never thought to ask]].)
* In the Literature/CiaphasCain 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 Creator/{{Aesop}}'s fables, a literal AssInALionSkin accidentally outs himself by braying. In another one, AWolfInSheepsClothing accidentally outs himself by howling (although in other versions, the disguise [[GoneHorriblyRight works too well]] and he [[IronicDeath ends up slaughtered for food]] [[KarmicDeath by the shepherd]]).
* In ''Going Down for the Count'' by Creator/DavidStukas, the eponymous Count Siegfried von Schmidt has blue eyes and is an [[AssholeVictim 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.
* Creator/AgathaChristie plays with the trope sometimes.
** This proves to be a fatal flaw in ''After the Funeral'', a Literature/HerculePoirot 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 [[HeKnowsTooMuch 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. [[spoiler: 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'', [[spoiler:a member of a criminal gang]] wears smart and expensive clothes, but [[spoiler:her shoes are old and cheap]]. That leads to Poirot fighting out she’s not [[spoiler:a noble if impoverished lady she pretends to be]].
** In a 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… [[spoiler:but she is one inch shorter and has to wear high heels, while the Duchess wears low heels]]. It doesn’t end bad for her, though.
* In the first book of ''Literature/CodexAlera'', 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 ''Literature/HandOfThrawn'' duology, Moff Disra comes up with a plan to make it appear as if [[Literature/TheThrawnTrilogy Grand Admiral Thrawn]] is still alive in order to run TheRemnant from behind the scenes. To this end, he, a ConMan named Flim (disguised as Thrawn), and a former Imperial Guardsman named Grodin Tierce present Flim as Thrawn, who manages to fool pretty much 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 Literature/CliveCussler novel [[Literature/DirkPittAdventures 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 [[spoiler: is actually Admiral Erich Hiebert, a wanted Nazi war criminal who [[DeadPersonImpersonation 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? [[spoiler: 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.]]

[[folder:Live-Action TV]]
* ''Series/DoctorWho'':
** In "The Chase", the robotic Doctor refers to Vikki as 'Susan'; not knowing the Doctor had a new teenaged companion.
** In "The Faceless Ones", Jamie is captured by the shape-shifting Chameleons and replaced with an imposter--who does not have the real Jamie's Scottish burr.
** In "New Earth", Lady Cassandra (who speaks in a rather posh fashion) takes 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". {{Hilarity ensues}}. She's later outed because (on top of the hilarity) she is not worried about the victims.
** In "Tooth and Claw", the Doctor accidentally ends up in the Scottish moors. The moment he realises they're in Scotland he switches to a Scottish accent (though not the actor Creator/DavidTennant's natural Scottish accent) and pretends to be a Scottish physician [[ContinuityNod named Dr. James McCrimmon]] so that Queen Victoria doesn't shoot him. Later at dinner he slips back into an English accent and Victoria calls him out.
** In "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, and real Sarah hates ginger beer.
** Two telesnaps from episode six of "The Evil of the Daleks" show that this trope applied. When the Doctor named the three Humanized Daleks ([[OneLetterName using the Greek alphabet]]), he drew the lowercase letters on their shells. So when a Dalek bearing an ''uppercase'' Omega turned up, the Doctor knew it was a trap.
** Downplayed in "The Poison Sky". The Doctor immediately notices that Martha has been replaced by a clone, but the differences are so tiny, no-one without his [[BizarreAlienBiology bizarre alien senses]] and memory would pick up on them.
--> '''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... [[TwinThreesomeFantasy maybe not in front of]] [[AnythingThatMoves Captain Jack]].
* In ''Series/TheAdventuresOfSuperman'' episode "[[Recap/TheAdventuresOfSupermanS5E4TombOfZaharan Tomb of Zaharan]]", Clark notes that a telegram supposedly written by Lois and Jimmy did not use reporter's phrases.
* The "Datalore" episode of ''Series/StarTrekTheNextGeneration'' made clear that Data doesn't use contractions, while Lore can. In an inversion, even though Data is the person Lore is copying, Data was the younger of the two, and so technically "lost" the ability to use contractions. (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 ''Series/RedDwarf'' episode "Psirens", the impostor 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'.
* Tested in ''Series/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 the "body swap" storyline of ''Series/BuffyTheVampireSlayer'', Buffy had Faith's Bostonian accent on certain words. (No one really noticed in-universe.)
* Nicely done in ''Series/{{Merlin 2008}}'' when Morgana [[BackFromTheDead resurrects Lancelot]] from the spirit world, [[BrainwashedAndCrazy 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.
* ''Series/{{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 [[AlternateUniverse 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 [[spoiler: Tess was never given up for adoption]], he overlooks the fact that [[spoiler: 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.
* A season one episode of ''Series/{{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.
* In ''Series/LostGirl'', 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 marshmellows 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 marshmellows."
* In the season two finale of ''Series/{{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.
* In the season two ''premiere'' of ''Series/SleepyHollow'', 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''' pronounciation, something the real Ichabod would never do.
* ''Series/TheWildWildWest'''s "The Night of the Colonel's Ghost" has Artie impersonating Ulysses S. Grant in a bid to flush out a [[HesJustHiding 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.
* In the premier episode of ''Series/ThePlayer'', this happens multiple times. Kane spots an assassin [[spoiler: dressed as hotel staff because he's wearing the staff jacket but not the right pants.]] At the end of the episode [[spoiler: 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.]]
* In the ''Series/KCUndercover'' three-parter (or four-parter, depending on where you see it, as the hour-long first part was shown internationally as two half-hour instalments) "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 imposter 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.
* Used in the HalloweenEpisode of ''Series/PowerRangersDinoCharge'': One of the six Rangers has been replaced by an EvilTwin duplicate, and [[MissionControl 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: [[spoiler: [[FishOutOfTemporalWater Koda]] is the only Ranger on FirstNameBasis with her, and he had repeatedly called her "Ms. Morgan" instead]].
* ''Series/StarTrekDeepSpaceNine:''
** 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 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 while playing springball; when O'Brien says 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.
* One episode of ''Series/PainkillerJane'' 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 [[BluffTheImposter 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 an episode of ''Series/{{The Librarians|2014}}'', 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.
* In ''Series/TheFlash2014'', 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 ([[spoiler: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 OhCrap 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 ''Series/{{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.
* ''Series/{{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.
* On ''Series/{{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 ''Series/StrangerThings'', Joyce knows the body at the morgue is not her son's because TheConspiracy 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.
* ''Series/MontyPythonsFlyingCircus'' 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.
* The AdaptationExpansion of ''The Affair at the Victory Ball'' in {{Series/Poirot}} has it as the ultimate clue that leads to the murderer’s arrest. The murderer [[spoiler: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 [[spoiler:he is left-handed while the victim was right-handed]]. When one of the victim’s friends remembers it, the murderer is caught.

[[folder:Mythology & 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.
* ''Literature/TheBible'': 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.

[[folder:{{Video Games}}]]
* In ''VideoGame/SaintsRowTheThird'', The Boss attempts to impersonate [[spoiler: Cyrus, the leader of STAG,]] but pretty much fails to act appropriately in any way. Given how poor the act is, it takes The Boss a surprisingly long time to get caught.
* For a period of time in between major updates, Spies in ''VideoGame/TeamFortress2'' suffered from this when disguising. Unlockable weapons for some of the other classes had been introduced, but Spies taking the disguises of other players of that class would only show stock weapons. Unlocks such as the Ubersaw and Blutsauger for the Medic or Backburner and Flare Gun for the Pyro were astoundingly popular choices and anyone not using them was suspect. For instance, Medics who appeared carrying basic Syringe Guns were immediately suspected as Spies, making the disguise even more difficult to use convincingly. This disguising oversight has since been patched out.
** A trait of a poor spy would also be always having their disguise carry the default weapon; it's very odd indeed to see a Medic carrying a syringe gun over the medi-gun, or an enemy spy not to have a knife out. [[note]]This switch can be made by changing to your secondary and pressing "B".[[/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 (which has long since been patched): 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.
** Spies disguised as Scouts are also prone to "forgetting" how the latter class moves; Scouts are noticeably faster than other classes and can double-jump, which disguised Spies cannot.
* At one point in ''VideoGame/{{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 ''VideoGame/ShinMegamiTenseiIV'', 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.
* [[spoiler:Your clone]] in the ''Citadel'' DLC for ''VideoGame/MassEffect3'' 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 imposter is going to be able to fool, say, Admiral Hackett for even a minute.
** The imposter ''did'', to their credit, remember that [[spoiler: despite being [[CloningBlues a clone]]]] they would need to replace the original's recorded fingerprints with their own, and arranged a complex scheme to do just that.
* ''VideoGame/StarTrekOnline'': The side mission "Standoff" has the [[TheRemnant 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 ''VideoGame/BanjoTooie'', Mingy Jongo refers to Banjo by name (as opposed to Mumbo referring to him as Bear).
* In the ''VideoGame/DarkSouls'' trilogy, [[ChestMonster 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, [[SpottingTheThread mimics breathe]].
* In ''VideoGame/BlazBlueCentralFiction'', Phantom attempts to manipulate several characters during Act 1 by creating illusory versions of other characters. However, Jin sees through a false Ragna because [[ArchEnemy 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.

* In ''Webcomic/TheDragonDoctors'', "Elizabeth", the leader of a gang of thieves, disguises herself as [[spoiler:Goro]] [[http://dragondoctors.dhscomix.com/archives/comic/ch-10-page-30 with a specialized identity theft spell that hides her previous forms.]] Unfortunately for Elizabeth, [[spoiler:[[http://dragondoctors.dhscomix.com/archives/comic/ch-10-page-36 Sarin instantly noticed that she couldn't see]] [[GenderBender Goro's old male form.]]]]
* When Destania from ''Webcomic/DanAndMabsFurryAdventures'' pretends to be [[spoiler: 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.
* Parodied in ''Webcomic/{{Oglaf}}'' with the slutty master of disguise, whose otherwise flawless attempts at impersonation are always marred by his insistence on dressing as a [[SexyWhateverOutfit slutty version]] of the person he's impersonating and claiming that he "won't sell out" when asked about it.
* ''Webcomic/PlanetOfHats:'' 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 ''Webcomic/RustyAndCo'', 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 ''Webcomic/SamAndFuzzy'', the only clue that the mole in Sam's reconstructed Ninja Mafia is [[spoiler:the shapeshifting Jess masquerading as Mr. X]] is that [[spoiler:when she's transformed, [[http://www.samandfuzzy.com/1382 X's missing arm]] is on the [[http://www.samandfuzzy.com/1447 wrong side of his body.]]]]
* In Season 16 of ''Webcomic/SurvivorFanCharacters'', 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.
* Changelings in ''Webcomic/StarMares'' are bad at colors. The Nightsisters in particular have a problem getting the eyes right.
* In ''Webcomic/InOurShadow'' 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 an escaped a situation [[NoOneCouldSurviveThat 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.

[[folder:{{Western Animation}}]]
* In ''WesternAnimation/JackieChanAdventures'', 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." TruthInTelevision. There is no equivalent to the English "J" sound in the Spanish alphabet (their "J" sounds like an English "H"), so many Spanish-speakers even those who are basically bilingual still talk about watching [[Film/{{Jaws}} Yaws]] or [[Series/JudgeJudy Yudge Yudy]].
* ''WesternAnimation/CodenameKidsNextDoor'':
** One episode, when Numbuh One is trapped in a LotusEaterMachine, he realizes what's going on 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!"
* ''WesternAnimation/MyLittlePonyFriendshipIsMagic'':
** It's the principal failing of [[spoiler: the Changelings]], as "getting into character" isn't their strongest suit. More specifically, [[spoiler: 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, [[spoiler:a Changeling]] mimicking Derpy Hooves forgets to do the FishEyes. [[spoiler: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.
** Episode "Spike at Your Service" features Spike [[IOweYouMyLife 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 the real Timberwolves show up and Spike end up having to save Applejack for real.
* In an episode of ''WesternAnimation/BatmanTheAnimatedSeries'', Clayface tries to fool a security guard by shifting form into the likeness of the guy's boss, but the guard is tipped off when he realizes Clayface doesn't have an accent. (''Then'' he remembers his boss is in Hawaii, and Clayface decides to skip the pleasantries and knock him out.)
* Clayface does it again in an episode of ''WesternAnimation/JusticeLeague'', 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, [[IronicEcho "yo."]]
* On ''Star Wars: Detours'', the Decoys are supposed to look identical to Princess Leia in every way, but they're missing [[ImprobableHairstyle her most defining feature]].
* In ''WesternAnimation/SpiderManTheAnimatedSeries'' 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 been flipped.)
* Zigzagged in one episode of ''WesternAnimation/EdEddNEddy'' (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. [[spoiler:Eddy's reaction is, or course, a {{Foreshadowing}} to the movie, where it's discovered how much he's ''really'' terrified of his brother.]]
* In an episode of ''WesternAnimation/TransformersPrime'', [[TheBigGuy Bulkhead]] manages to spot a [[TheMole fake Wheeljack]] by tricking him into telling a war story about Bulkhead, who was not actually present at 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.
* In the ''WesternAnimation/AdventuresOfSonicTheHedgehog'' 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.
* In ''WesternAnimation/JohnnyTest'', Dukey has to figure out which of two Johnnys are a robot. When they answer the first two questions perfectly, he asks a math question. One Johnny answers immediately, and Dukey blasts him. The reason being Johnny has to use his fingers when he's asked such a question.
* ''WesternAnimation/PinkyAndTheBrain'': When Brain decides to take over the world by impersonating UsefulNotes/AbrahamLincoln, he's not worried that people will notice that he doesn't sound like the real Lincoln because Lincoln died before voice recording devices were invented and Brain doesn't believe there's any living person old enough to have heard Lincoln talk. The oldest living American proves him wrong about the last part.
* ''WesternAnimation/StaticShock'': In "Duped", the shape-shifting criminal Replikon kidnaps [[Music/BackstreetBoys 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.
* ''WesternAnimation/ArabianKnights'': 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.
* ''WesternAnimation/TheSimpsons'': 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 is 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.
* When master of disguise Anyface exposes himself as an impostor of Paul [=McCartney=] in ''WesternAnimation/TheBeatles'' episode "No Reply" as a bevy of fangirls chase him, Ringo points out "A Beatle would have known enough to run!"
* In one episode of ''WesternAnimation/{{Cyberchase}}'', Digit attempts to impersonate [[SpellMyNameWithAThe (the)]] [[BigBad Hacker]] using an obviously robotic suit that [[PaperThinDisguise 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 [[FashionableAsymmetry his pocket protector]].

[[folder:{{Real Life}}]]
* OlderThanFeudalism: [[http://en.wikipedia.org/wiki/Shibboleth Shibboleths]] originate from [[Literature/TheBible 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 exist in Hungarian, and many Hungarian speakers tend to confuse them.
** 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]]Most Orthodox Christians cross themselves right to left, Catholics (like the Ustasha) cross themselves left to right.[[/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 [[JapaneseRanguage "Lollapalooza"]].
* During World War 2, any attempt of the Germans to pass forged documents to the Soviets ended up been exposed. The fakes were recognized even by ordinary soldiers. Only after a long time it became a well-known secret. Paper clips in the Soviet Union were made of ordinary steel (and in war they were rusty), and German paper clips (including the forgery of Soviet documents) used stainless steel.