Fry: Flexo, shoot Flexo!
The heroes encounter a situation where the villain is an imposter of one of their own and/or a sympathetic character. The heroes must find out about the imposter and expose him/her to stop him.
Typically, the situation will involve the impostor and the real person standing side-by-side, both claiming to be the real one, and the other heroes must use their wits to identify who is who, usually by finding a quality that the faker doesn't have (in comedic examples, a positive quality). Or the real person may ask that their friend shoot both of them just to guarantee they get the imposter (and it's almost inevitable if the person has a super-healing power), which usually results in the heroes shooting the other one, because the impostor wouldn't be noble enough to suggest making the Heroic Sacrifice. This is often parodied these days where the imposter suggests it, knowing they'll assume the noble act to mark them out as the original and sometimes double-parodied when this ends up outing him as the fake since the real person wouldn't be so noble.
In videogames, often the two clones will be desperately attempting to beat the crap out of each other while the player struggles to figure out a means of telling them apart, often with one tackling the other, punching him a few times until the pair rolls over and the person on top switches, ad nauseam (which conveniently allows a very short looping animation to represent the whole fight).
Speculative Fiction variants can get really confusing once you add in the possibilities of magic and/or Applied Phlebotinum: For example, the victim of a "Freaky Friday" Flip must find a way to convince their friends that the person who looks like them really isn't, while the impostor is trying to convince the same friends that the victim is trying to initiate a body swap instead of undo one.
A common subversion is for the protagonist to either shoot in a blind guess that turns out correct, or simply shoot both and see who gets madder. In both situations, the victim of the imposter is likely to be incensed that the hero couldn't tell him from his doppelganger.
Another subversion is for neither of them to be an imposter but in fact both are two parts of the same person split with Applied Phlebotinum; see Evil Twin and Literal Split Personality. If they are two (visibly) different people but both claiming to be the 'real' whatever-position-would-be-relevant (captain, mother, president, owner, etc), see Judgment of Solomon.
A more comical subversion is when the imposter looks nothing like the person they are imitating, but people still act like they are identical, even if they haven't bothered with a Paper-Thin Disguise. The less the two look alike in this situation the more likely it is that no one can spot the difference.
The real person's nervous tic can also be useful in exposing the imposter.
Compare Cover Identity Anomaly, Imposter Forgot One Detail (where the imposter's disguise has one subtle flaw), Impostor Exposing Test, and Twin Test (which may involve a person impersonating their identical sibling). See also: Evil Twin, Bluff the Impostor, Confronting Your Imposter, Ten Little Murder Victims.
- During the Chunin Exams, two different characters use ninjutsu to disguise themselves as Naruto himself in the same episode, but one is identified as an imposter because he was left-handed (his throwing knife holder was on the wrong side), and the other reveals himself as a fake by repeating a long, complicated Trust Password that the real Naruto would never be able to remember.
- During the Fourth Shinobi War an army of Zetsu clones disguise themselves as members of the army, even faking their chakra, and start picking off the enemy. Some are spotted based on mistakes in their cover identity, but ultimately only Naruto can identify them en masse due to his ability to sense their evil intent.
- In one episode of Ghost in the Shell: Stand Alone Complex, a woman who has obsessively studied Pazu has a duplicate of his cyborg body made and her brain put into it; the two then fight and one ends up dead; the incident is not brought up for the rest of the series, implying that either the real Pazu won, or the fake was so good that she simply took his place. Judicious use of the pause button, combined with paying very careful attention to details such as wounds inflicted at the start of the fight (when viewers still know which Pazu is the real one), make it clear that the real Pazu won the fight. However, the show lets you figure it out for yourself instead of spelling it out for you.
- In Delicious in Dungeon, the party is confronted by a group of doppelgangers that base their appearance on the party members' perceptions of each other. Laios is the only one that is above suspicion, as all his doppelgangers look obviously fake. Through a process of elimination, they manage to narrow down the other clones to only a few options, but for the final ones, Laios decides they should all cook food to show that they're the real ones. In the end, Laios realizes who are the real ones by noticing little quirks in their behavior that they would never do:
- The fake Senshi takes as many harpy eggs from their nest as he can, which contrasts with the real Senshi's deep understanding and care for the ecosystem.
- The fake Chilchuck sits down in a random crate to peel vegetables, which contrasts with the real Chilchuck's paranoia towards any vessel that might hold tentacles and mimics.
- Marcille had a previous nasty experience where pouring boiling water out got her into trouble with an Undine; as Laios notes, the real Marcille is enough of a careless airhead to make the same mistake twice. The fake Marcille also mentioned they'd eaten merman eggs, a fact that the other members hid from the real Marcille, so she shouldn't know. But this flies over the the others' heads until the real Marcille points out that they'd never eaten merman eggs (or so she thinks).
- In a Mazinger Z episode, Big Bad Dr. Hell fabricates a robot seems just like The Professor Yumi. However it was quickly identified by Sayaka when she noticed the imposter's nails were black. Dr. Hell used that strategy more times, creating a robot looked right like a secondary character and going as far as building a robot resembled The Hero Kouji. They also were spotted sooner or later.
- That plot was partially reused in a Mazinkaiser episode. The Dragon Baron Ashura kidnapped Prof. Yumi and disguised himself like him. Sayaka suspected him nearly right away, though, because he tossed a birthday gift into a trash bin, and she told others her father would never do that.
- Something similar occurs in the climax of Read or Die's OVA. By paying attention, it's possible to note that the "real" Miss Deep is the winner before it's revealed as part of the plot.
- In an episode of YuYu Hakusho, Yuusuke is told that one of his friends is an imposter, and he must identify the impostor by punching them. He correctly chooses Kuwabara, but then reveals that he'd simply chosen the suspect who'd be best able to cope with being punched in the face (they're rivals who punch each other on a regular basis). And the one who'd most likely fall into the trap allowing an impostor to appear in the first place.
- Again the split was used in Ah! My Goddess, when Urd was split into her Demon and Goddess parts. Made easier when it turns out that Skuld had secretly put a mark on the goddess Urd.
- In an episode of Rockman.EXE Beast, an evil alternate version of Numberman shows up infiltrating the core group of friends. When the normal universe's Numberman arrives, obligatory hilarity ensues as the two attack each other identically, to such an extent that their Dice Bombs roll the same number. The problem is solved when it's realized that if they attack both Numbermen, the fake one would be forced to shapeshift, and then all present Main Characters can hit him at once. note
- A variant occurs during the Frieza saga in Dragon Ball Z. Captain Ginyu uses a last ditch move that puts his mind in Goku's healthy, stronger body, while Goku's mind is stuck in Ginyu's injured form. The real Goku has to convince Gohan and Krillin what has happened when they attack him in Ginyu's body.
- In Futari wa Pretty Cure, Poisonny impersonates Honoka at one point. When Nagisa has to pick the correct Honoka, all she can come up with is to ask them what her (Nagisa's) favorite food was, which is a question that has some problems. The Honokas proceeded to switch off saying accurate (and, for a time, increasingly negative) things about Nagisa, until the real one finally remembered that only she could read the diary in which Nagisa wrote that "my socks are a little smelly," a quotation that confused the fake. (The episode featured a Red Herring in the form of a perfume Honoka had made earlier in science club — as both Honokas pointed out, having or wearing the perfume proved nothing, because the fake could have just stolen the bottle.)
- Subverted in Fullmetal Alchemist when Mustang and Hawkeye are confronting Envy. Envy pretends to be Mustang in front of Hawkeye. However, after a brief exchange, she points her gun at him and says she knows he's not Mustang because he was calling her Lieutenant, while the real Mustang always calls her Riza when it's just the two of them. Envy expresses surprise that the two of them are that close, at which point she tells him she was lying, but he'd already given himself away.
- Played straight in the 2003 anime version. In the two-part episode "The Other Brothers Elric", the Tringham brothers pose as Ed and Al. In a variation, the Tringhams don't even resemble the Elrics (save for hair color), but no-one in the town knew what the Elrics look like; they just know their reputation.
- When Envy poses as Ross, Hughes knows it isn't her when he notices she didn't have a mole under her left eye.
- In Zatch Bell!, one of the characters has the ability to change into other characters... badly. He often has a way too big nose or forehead, but everyone but the one he transformed into is oblivious to the differences.
- In "Will the Real Oak Stand Up?", with James from Team Rocket being the impostor. Interestingly, James was eventually discovered as the impostor not because he played his part badly but because he played his part too well: they were having a poetry contest, and James came up with overly-flowery poems to impress the judges. The poems were good, but they weren't even close to Professor Oak's actual poems, which were typically only two or three lines but contained a "hidden lesson" that was absent from James' poetry.
- A later episode did the same thing, with the same imposter, with the same costume. They barely look alike. Nobody can tell the difference.
- The Main Characters usually have a hard time seeing through James and Jesse's disguises, no matter how bad they are. However, in one Tournament Arc, Jesse tried disguising herself as Nurse Joy (there were several Joys at the stadium to handle the massive number of Pokémon) and Brock smelled a rat quickly; he swoons over every Joy he meets, and could even tell them apart (as he explained earlier in the episode) so it was easy for him to recognize a fake Joy, it seemed.
- He's also spotted a fake Officer Jenny on at least one occasion, specifically because he only went ga-ga over the real one. That is, he subconsciously knew the impostor, despite being physically identical to all the other Jennies out there, was in fact simply a well-disguised man.
- In another episode, Pikachu is surrounded by many ghostly illusions of Ash, with the real one lost among them. He settles the matter by shocking all of them, making them disappear until only the real Ash is left.
- Made fun of in Lupin III: Part II episode 65: Mr. X turns himself into a clone of Lupin, and Jigen decides to determine the imposter. One of the Lupins passionately declares that he would rather die by his friend's hand than be killed by the other Lupin; Jigen immediately shoots him, declaring that (to Lupin's embarrassment) the real Lupin would have panicked and begged for his life rather than stoop to such poeticisms. For a brief moment, Lupin imitates Mr. X's vocal mannerisms to Jigen and Goemon's concern, but this is quickly revealed to be a joke.
- In the Alabasta arc in One Piece, Mr 2: Bon Kurei assumes the form of Usopp to fool Vivi. He fails because the crew was on guard, having met him before and had prepared a special sign to reveal their true identities. Not only that, but Bon Kurei in the guise of Usopp acts callous when Karuh is shot. Vivi knows that the real Usopp would never treat Karuh like that.
- In Sumomomo Momomo, Iroha uses her clan's ability to turn into Momoko, voice and all. She gets touchy feely with Koushi when in the presence of Sanae so Sanae will not interfere with Momoko and Koushi's future marriage. The real Momoko shows up and Koushi figures the right one because Iroha is grabbing onto his arm which was just injured the previous episode and the real Momoko would know about that since she treated the injury. The real Momoko thinks the fake one is an assassin and quickly blasts her away. Iroha shows up about 5 seconds later without the disguise, but very bruised. Nobody ever figures it out or asks about it again.
- Subverted in a filler arc of Bleach, specifically anime episode 326. While Captain Hitsugaya is fighting Reigai-Momo Hinamori, the real Momo appears and attacks Reigai-Momo. Hitsugaya has to figure out which one is the real Momo so he can defend her from Reigai-Momo's attack. Then, once he makes his choice, to his surprise the Momo he's protecting stabs him, revealing that both of them are Reigai-Momo. They then team up to try to kill him.
- In Soul Eater, Maka becomes trapped in a room with a demon disguised as Soul, and the real Soul trapped in a box inside the room. The Fake!Soul explains to Maka that she has to open the box to get free (allowing himself to escape) with the real Soul's voice unable to reach her to warn her of the imposter. Maka is almost convinced until she points out that he had closed the door behind her, knowing they would be trapped, and that the real Soul would've immediately warned her to leave.
- JoJo's Bizarre Adventure:
- In Stardust Crusaders, the group is on a ship and knows there's an enemy Stand user aboard, but whoever it is hasn't shown themselves. Jotaro, who's just finished smoking a cigarette, claims he's figured out how: when a Stand user inhales smoke, a vein pops out on their nose. Reflexively, all the heroes put their hands to their nose to check... and so does the ship's captain. In fact Jotaro was lying, no such effect exists, but the captain had given himself away with that action.
- At one point in Diamond is Unbreakable, Okuyasu has to figure out between two people dressed as Speedwagon Foundation members which is an assassin trying to kill Joseph, who's in the same room, with his stand (while the two look nothing alike, Okuyasu had never seen the assassin before and only heard him talk through his stand, and thus doesn't know what he looks or sounds like.) When the assassin discreetly preps his stand to attack, Okuyasu quickly punches him out, and when asked how he knew, proclaims that he's not that smart and was just going to punch out the other guy too.
- Fairy Tail: Heroic version. Earthland Erza manages to trick Faust and his soldiers before the Edolas-Erza shows up. Edolas-Erza cuts her hair later to keep it from happening again.
- In The Seven Deadly Sins, the heroes get confronted by several magical duplicates of Hawk and Elizabeth. Meliodas simply smacks all of the Hawks at Super Speed. The real Hawk gets injured (and calls Meliodas out on it), but the fakes disappear. Meliodas then challenges all the Elizabeths to jump as high as they can. The fakes agree and do it, but the real one refuses because she is wearing a skirt and Meliodas stole her panties earlier.
- My Hero Academia: After the UA students are separated during the Provisional Hero License Exam, Midoriya is alone against a team of students from another school when Uraraka shows up, and the two of them escape. Then Uraraka tries to tag Midoriya from behind and eliminate him from the test... and he swats her hand away without even looking. He knew all along that she wasn't really Uraraka, because she didn't use her powers to levitate when she fell off a ledge, and Uraraka would've never revealed herself to the enemy without a plan. Perhaps it would've been better to impersonate somebody Midoriya was less familiar with instead of his best friend, but the shapeshifter's power works by drinking the blood of the person they change into, and she extracted a pint of Uraraka's blood in the previous story arc but didn't have any other UA students' blood yet. There was also a visual clue for the readers to spot: the fake Uraraka was wearing her helmet, but the real one lost hers during the same attack that separated her from Midoriya in the first place.
- Nagasarete Airantou: One chapter is about Machi trying to recapture a shapeshifting Genjumaro along with Ikuto and Suzu. It ends up with trying to identify it when it transformed into Mei-Mei. Ikuto manages to find it by making up a detail on her body. Except Ikuto was actually the Genjumaro. And the fake Mei-Mei was real Ikuto knocked out and transformed. Suzu suspects this since he was oddly accepting of magic during the search. Another unmentioned hint to the readers is when he wasn't nosebleeding while Machi was drying her clothes.
- Yaiba: Chamaleon Bonaparte, a chameleon man, transforms into a perfect copy of Yaiba, which forces the hero to guess his identity. Musashi fails to lure him out with a live bug, but Sayaka does by asking them both a math question (the real Yaiba gives the wrong answer). In the anime adaptation, the villain tries again with Sayaka, but is eventually spotted when Yaiba gropes both girls, with the real Sayaka punching him in response.
- Haruhi Suzumiya: Koizumi notes that as he's basically a tool of Haruhi's subconscious, he can easily identify her in any situation. Unfortunately, the reason this comes up is because Kuyoh is trying to kill someone who appears to be Haruhi—and Koizumi confirms that yes, it is her.
- Fire Force: Parodied when Sister Iris faces Tamaki and an imposter. Despite the fact that the imposter cannot demonstrate Tamaki's powers and doesn't even attempt to disguise his voice, Iris says she can't tell the difference, to Tamaki's frustration. It's only when Tamaki ends up tripping and gets stripped naked as per usual that Iris finally realizes it's her friend and the doppelgänger tries to run away.
- In episode 16b of Jewelpet: Magical Change, Sapphie has had so many clones made of her that Airi and her gang can't discern which is the real one. To solve the problem, they hold a tournament with all sorts of games (among them a quiz, air hockey, and jankenpon) and declare whoever is the last Sapphie will be considered the real one.
- In episode 27 of Happy Heroes, a monster creates an Evil Knockoff of Happy S. and the other Supermen have to figure out which is which. An Impostor Exposing Test where both Happy S.'s are asked questions ends with the evil Happy S. winning and being mistaken for the real one, which catches the real Happy S. off guard.
- The page image comes from an Archie Comic where Dilton and his friend discover a meteor from space that is actually an amorphous Voluntary Shapeshifter that feeds on electricity. Its cover is blown when Danni spots the large orange patch on its back that it can't seem to hide.
- Spider-Man: This happens a lot when the Chameleon is involved. (He is a Master of Disguise, after all.)
- A Fantastic Four and Spider-Man story resolves the situation of the Chameleon impersonating Spider-Man in a distinctive manner. The Thing, holding one in each hand, throws both several meters into the air. The Chameleon reveals himself by screaming in terror and the Human Torch flies up to catch him while the real Spider-Man, who is used to this kind of situation, calmly shoots a webline to swing to safety.
- More than once, the Chameleon has wondered how it was possible Spider-Man automatically knew it was the Chameleon disguised as...Peter Parker.
- One time after he discovered the hero's identity (and the fact that he was Kraven the Hunter's half-brother, something which gave him his confidence back) he impersonated Spider-Man and tried to fool Mary Jane. She realized it wasn't Peter when he kissed her; as she said herself, "It made my skin crawl." (This led to what was probably the most humiliating situation in the villain's career. Spider-Man didn't need to do anything; she beat him senseless with a baseball bat.)
- The most humiliating might be when (after Peter revealed his identity to the world), the Chameleon infiltrated Avengers Tower as him, expertly fooling the various security scans. He then played at a dinner with Aunt May, eating some brownies and having some small talk while she knits. May then remarks about how "the real Peter only could have one or two almond brownies."
May: You'll be interested to know that Peter's Uncle Ben could never go to sleep without making sure every single door and window in our house was locked and double-locked. And that Peter's favorite cookies are ginger-snaps and he hates oatmeal raisins, even mine. And that my friend Emily Pollack hasn't ordered yarn from me in ten years since she retired to Florida, the dear.
Chameleon: You...you were testing me the whole time?
May: Heavens, no. I was confirming. I suspected you weren't Peter on the elevator ride up. After all...what kind of mother wouldn't be able to tell her own son from an imposter. Because that's what I am to Peter.
- The Chameleon rises up to attack...only to fall flat on his face as May drugged the cookies. When the real Peter bursts in, he finds Chameleon all tied up as May keeps on knitting.
- In Spider-Man: Life Story, an aged Peter and Miles Morales are on a mission and attacked by a Venom-symbiote infected Kraven. After defeating it, Peter notes "all my enemies are dead. Isn't that right... Otto?" Dr. Octopus demands to know how Peter figured out he had taken over Miles' body. Peter relates it was "the little things" such as "Miles" being more serious and calling him "Parker"; calling Kraven by his first name as if he knew him; the symbiote stopping an attack as it sensed what happened and laughing "well played, old friend." The clincher was that not only was Miles using technology more than he used to but it was rather outdated, as if designed by a genius scientist stuck in the past.
- Gold Digger plays with this trope.
- Shapeshifter Madrid arranges to disguise herself as the Heroine, Gina Diggers. She then arranges for the real Gina to act out of character in several suspicious ways (an out-of-date outfit, etc.), while trapping herself for Gina's companions to find. As a finishing touch, during the confrontation with Gina, she uses the "lock us both up" subversion to win the trust of the others.
- Later, one of Gina's friends (who happened to be Madrid's ex-husband) was able to determine she's the real one by telling her he'd fallen in love with her and asking if she loved him too. She apologized and said that while she valued him as a friend, she didn't feel that way about him, which convinced him she was the real one. He explained to Gina that one of Madrid's biggest flaws is that she never fails to tell someone what she thinks they want to hear.note
- Amazons Attack!: In a Wonder Woman (2006) tie in two Sgt. Steels have been discovered, and the government agency he runs need to figure out which is which. Finally, after a long interrogation, one of the Sgt. Steels in exasperation asks for a pen. The soldiers think it is for a handwriting test, but he instead points out that he has a metal arm, which doesn't bleed — and then swiftly stabs the other Steel in the 'metal' arm with it, showing the second Steel to be a shapeshifter when he shouts out in pain. This is subverted, however, in that the first 'Sgt. Steel' is ALSO an imposter, one who has taken on Steel's form to discover where the real one is; he just happens to be an imposter who's quicker at thinking on his feet than the second one. Fortunately, the first one is the good guy.
"Sgt. Steel": First, everyone knows that I have a metal hand. Second, metal doesn't bleed. Third, you're all fired.
- Somewhat complicated version in a Nick Fury comic: Fury is battling Baron von Strucker, the head of HYDRA in his soon to be Collapsing Lair, but he has to disguise himself as Strucker using a convenient masking device in order to commandeer a plane out. However, he also sets up Strucker's death by first disguising Strucker as Fury and then putting a second mask on Strucker so he's wearing his own face on top of Fury's. Result? HYDRA troops burst in and see two Struckers fighting. Fury-disguised-as-Strucker convinces the HYDRA troops he's the real Strucker by yelling louder and ordering troops to remove Strucker-as-Fury-as-Strucker's mask, so the troops comply. Strucker panics and dives into the alpha particle generator, dying. Fury-as-Strucker jets off. A bit of Fridge Logic: Fury wears an eyepatch, while Strucker wears a monocle. Where did Fury get two eyepatches and two monocles from?
- Sonic the Hedgehog (Archie Comics) had an extended version in which the changes of Antoine were revealed to be him having been replaced with his Mirror Universe counterpart, who had promptly set to political maneuvering and nearly arranged to become king of Mobius before Sonic finally Spotted The Impostor. (Antoine, meanwhile, had been dumped in his counterpart's place and had been doing his best to play evil to keep anyone from catching on.)
- In Supergirl (2005) Girl Power storyline, Dark Supergirl switches her costume with the original Supergirls at super-speed, in an attempt to fool Batman and Superman as to who was the evil clone. Superman tries to spot the imposter by punching both girls, assuming -wrongly- that the real one will not retaliate. Finally, the real Kara gets fed up with the situation, and tells Wonder Woman to use her Lasso of Truth.
- An early Batman serial strip had Batman disguise himself as a mob boss in order to free Robin — unfortunately, the real one came back earlier than expected, and the boss' henchmen had recently decided to get rid of their Bad Boss.
- An example occurs in the Batgirl Adventures Annual #1 comic where Batgirl is helping Harley Quinn track down Poison Ivy, who has been abducted. The villain manages to copycat Harley completely, from attire to voice, and Batgirl contemplates just beating up both of them. She finally figures out the real one when Harley uses her insult nickname for B(r)atgirl.
- In the final issue of a short-lived mid-70s comic named after and starring The Joker, he decided to hold the heavily-insured feline sidekick of a famous movie comedian for ransom. The comedian disguised himself as the Joker in order to retrieve it, and when the Joker's minions were faced with this trope the Joker suggested that they let the cat go and whoever it went to would not be him. When it went to the Joker instead, and while being arrested he protested that a cat couldn't be trained to go to someone other than its master, the comedian said "No cat except my million-dollar kitty!"
- A heartbreaking one during Marvel's Secret Invasion (the main mini-series): In Issue #8, Back from the Dead Mockingbird is confronted by her ex-husband, Hawkeye (who, at the time, was presumed dead and operating as masked hero Ronin). To prove she wasn't a Skrull, Hawkeye states a certain date, and asks Mockingbird what it meant. Turns out, Mockingbird had a miscarriage on that date and only she and Hawkeye ever knew she was even pregnant. This also served to tell Mockingbird who was under the Ronin mask.
- G.I. Joe:
- An early issue had Zartan trying to escape the Pit by disguising himself as various Joes... Until he tries to imitate Gung-Ho right before the real one shows up. When both of them end up in front of Sgt. Slaughter, he decks one of them, which shifts back to Zartan. Slaughter says it was just a lucky guess.
- An early issue of the IDW reboot has him try to get into the team disguised as Snake-Eyes, only to get clocked by Duke. Duke didn't know he wasn't really Snake-Eyes, but was simply suspicious: If it had really been Snake-Eyes, he'd have easily blocked or avoided the punch.
- Shows up extremely often in Diabolik due the titular Villain Protagonist having invented Latex Perfection. It's usually just a question to pinch someone's face to check for a mask, but sometimes even that it's not enough (for example, Diabolik may have an accomplice to impersonate someone with a different corporature, or look sufficiently like someone else to use different means).
- Other times the spotting is made more complicated by the target preventing the police from doing the face check for some idiotic reason, something that always drives Ginko mad.
- A scientist once invented a machine that could detect the presence of Diabolik's masks. At the end of the issue, Diabolik had destroyed the machine, killed the scientist and stolen the blueprints.
- One of Diabolik's impersonations was that of Walter Dorian, a rich guy who looked just like him that Diabolik replaced to have a civilian identity (upon his second arrest, the one where they found out his real face, Diabolik ditched this as useless and confessed his murder).
- Funny enough, Diabolik has been the spotting one in at least two occasions, where lookalikes hired by the mob impersonated Eva Kant to keep him distracted while they robbed him. The mob instructed the actresses to feign amnesia or being ill to justify the differences in personality that would have caused Diabolik to spot the difference at once. In the case of the fake illness, Diabolik was ultimately able to spot the imposter, but the amnesiac one was so good Diabolik had no idea until she confessed after learning the mob killed her lover (the surgeon that made her into an Eva lookalike).
- Examples from the Disney Mouse and Duck Comics:
- Mickey Mouse Comic Universe stories featuring Miklos, the Grey Mouse elevated this trope to an art form, as Miklos can do a perfect Mickey Mouse impression, and looks just like him with grey fur (hence the nickname):
- In his debut in "Mickey's Dangerous Double" the police gets the both of them and promptly enlists Pluto, only to find him out of commission due his crush on a mannequin dog. They quickly asks Minnie, who first tells the right one (that the reader can recognize from the clothes) but then changes her mind. Numerous other attempts follow (including one relying on Mickey loving a cake that give a stomachache to everyone else that should have worked, except O'Hara got them the wrong cake, resulting in a double stomachache) until they end in a rainwater tank, at which point the Grey Mouse is unmasked thanks to him using washable dye;
- In "Mickey Mouse and the Grey Scourge", Mickey's friends are enlisted to try and spot the right one but they fail (with Minnie once again getting the real Mickey but getting convinced by Clarabelle it was the other), and are on the verge of a fight when Casey shows up with Pluto, who this time is not out of commission;
- In the 2014 story "Mickey Mouse and the Seven Boglins" Miklos has a more complex plan than usual, and for a while even Mickey is convinced of being the imposter (it helped he had been duped into taking fake vitamin pills that dyed his fur red and kept him unable to think straight), with the reader not being informed of which one is the fake until Minnie, once again, realizes the switch. This time, however, spotting the imposter is easy, as Minnie (who has evidently learned from the previous encounters) has tricked the fake into getting a tattoo and when comes the time to tell the right one she's quick to ask which one has it.
- In the Disney Ducks Comic Universe this trope usually involves Paperinik stories, as he is a Master of Disguise and some of his opponents are just as good-or, in one case, better:
- The disguise expert better than Paperinik is the Trasformista (that's Italian for Master of Disguise), whose modus operandi was to disguise himself as the target of his heist, walk in his home/business, and rob them blind. He was first arrested when he disguised himself as Donald, who he had heard was out of town, not knowing that Donald is actually Paperinik's Secret Identity and he had said he would be out of town to cover for his absence while he surveilled the place as Paperinik (cue a bemused Paperinik fly in, arrest and unmask the fake, and leave).
- In a Paperinik New Adventures story he infiltrated the presidential palace of Belgravia as Grigorji Grimka, the son of th president, who was collaborating after being nearly kidnapped by Belgravian rogues... Except Grigorji was an idiot who forgot to tell Paperinik he's in an Arranged Marriage with a woman who is allergic to flowers (hence she spots him. Thankfully, she's a loyalist), he has two pet tigers (who promptly recognize the switch from his smell and attack), and he's actually in love with one of his bodyguards, who he told about the switch, without knowing she's with the traitors. Also, in the same story, president Nestor Grimka himself has been replaced by the traitors' leader because, as much as Belgravia is devoted to cause wars to sell weapons and possibly conquer the world he's not stupid enough to want his market destroyed and draws the line at some kinds of crimes, and when he sees the fake Grigorji coming to Belgravia he's convinced the rogues have his son hostage and gives up the information they need to proceed with their plan.
- Mickey Mouse Comic Universe stories featuring Miklos, the Grey Mouse elevated this trope to an art form, as Miklos can do a perfect Mickey Mouse impression, and looks just like him with grey fur (hence the nickname):
- The Maze Agency: In "Two Wrong Rhodes", three women come forward all claiming to be lost heir to a fortune, and Jen and Gabe have to work out which one is genuine.
- Mr. Natural, set upon by a horde of admirers, ducks into a store and emerges in disguise in a garish costume change - then encounters someone looking exactly the same, a guru named Holy Ned, who accuses him of stealing his look. Then three or four more identical guys show up. As they argue, Flakey Foont shows up, looking for Mr. Natural to give him money he owes him, and they all excitedly claim to be him. As they all stand identical in a row, a caption asks the reader "Which one is the real Mr. Natural?" Answer: none of them! He'd taken off to put the moves on the local hippie girls.
- Power Pack: in "X-Men and Power Pack #2" of the all-ages series, Mystique impersonates Jack Power in order to escape the heroes. At Beast's suggestion that Mystique can only mimic a person's appearance but not their powers, Katie fires a salvo of energy balls at both Jacks, forcing the real Jack to assume his cloud form in defence while Mystique remains the same.
- When she is in someone else's form, Mystique's eyes usually flare yellow when she is tired, excited, angry, or about to shapeshift again.
- While she can copy someone's appearance, Mystique can't replicate powers. Thus, all it takes is seeing, say, Cyclops not firing eye beams or Kitty Pryde not phasing to realize who this is.
- Depending on the Writer, Wolverine (or others with heightened senses) can sniff out Mystique but other times, they'll be caught off-guard. Likewise, sometimes son Nightcrawler and foster daughter Rogue are able to somehow tell it's her but other times can be fooled like everyone else. Perhaps justified as occasionally, Mystique lets them tell in order to get close.
- Mystique used the "Shoot us both!" move when she and the SWAT team commander she was imitating were surrounded by SWAT officers; the cops obeyed, one fell, the other didn't. When a cop asked "Why are you still standing, sir?", "he" replied, ("His" eyes flaring yellow) !I just moved my vital organs into my lower body.....".
- Even without Mystique, this happens a few times to X-Men:
- Several of the team are at a beachside cafe when Gambit comes up. Everyone is shocked when Rogue tackles him over a cliff but when they land, "Gambit" turns into a Skrull. Rogue brushes it off as, having been raised by Mystique, she can tell a shapechanger.
- The X-Men are fighting the Starjammers who they think are being mind-controlled and thus holding back. Corsair blasts Storm and gloats that "these Earthers aren't so tough!" Storm immediately notes how odd a phrase that is as "Corsair was born on Earth and proud of it!" The X-Men realize these are really Skrulls and thus can cut loose.
- Visiting the mansion, Banshee is in a hallway corner when Psylocke exits Xavier's personal study. Banshee is less thrown by her being in an off-limits area than how he was able to hide in the shadows five feet away from a ninja-trained telepath. This leads to the discovery almost all the X-Men have been replaced by the Phalanax.
- More than once, Wolverine has suddenly sliced up what seems to be a normal person only to reveal it to be some sort of robot and saying "it didn't smell right." Wolverine was able to figure out the Dark Phoenix the X-Men were fighting was an illusion created by Mastermind because he couldn't smell her. Mastermind also made the mistake of shooting Cyclops with a silencer-equipped gun, not realizing Wolverine would be able to hear it.
- Laff-A-Lympics: During a relay race in "The Meet at Mount Ono", the Great Fondoo creates duplicates of Huckleberry Hound so Quick Draw McGraw won't know who to pass his team's rod to. Quick Draw eventually figures out who the real Huck is by having them sing "Oh My Darling, Clementine". The real one is more off-key than the imposters.
- Secret Invasion: Avenger Crusader (who is actually a Skrull who decided to live as a human super hero) is in the Avengers' commissary, with a plate of kiwi fruit, strawberries and pickles. Together, the combo approximated the taste of a favored Skrull fruit. He realizes the Avengers have been infiltrated by (other) Skrulls when he sees Hank Pym serve himself the same combo.
- In one issue of Usagi Yojimbo Gen gets lost in a forest haunted by nine-tailed foxes and runs into Usagi, and suspects he's a fox when another Usagi shows up. After fighting them both for a bit he realizes they're both nine-tailed foxes and runs for it.
- In a Richie Rich comic book story, Mr. Rich is replaced with an impostor, and when the real Mr. Rich stands beside his impostor, both claiming to be the real Mr. Rich, they are both tested by lighting up a pipe and smoking it. The real Mr. Rich does this without any problem, but the impostor ends up coughing when he inhales from the pipe.
- Wonder Woman (1987): Heading to rescue Steve Trevor from shapeshifting Durlans, Wonder Woman and Captain Atom know who they're dealing with. When they're separated, each is approached by a Durlan posing as the other but see through it fast. In Diana's case, she asks "Atom" if Captain Nate Adam was with Trevor, the Durlan confirming it...not knowing Nate is Captain Atom. In Atom's case, he's able to quickly see that "Diana's" lasso isn't glowing.
- In an earlier issue, a Durlan invaded a secret military base. When a helicopter starts taking off, General Eiling believes the Durlan is posing as the pilot. To his surprise, Atom yanks one of the gas tanks off of the copter and then tosses it into the blades, which slice the Durlan apart. Atom explains he's flown that type of helicopter before and knew it only has two fuel tanks, not three.
- The Iznogoud story "Fairy Tale" sees the title character recruiting hapless apprentice fairy Blunderbell to transform him into Caliph Haroun el-Plassid so that he can replace the real Caliph as head of state. However, she transforms the sleeping Caliph into a copy of Iznogoud instead; the copy then wakes up and immediately gets into an argument, then a fistfight with the original over which of them is the real Iznogoud. Blunderbell tries to resolve things with another spell, but only succeeds in transforming both Iznogouds into copies of the Caliph - and then she turns one copy of the Caliph into two copies of Iznogoud!
- In a Gold Key Looney Tunes comic book story featuring Bugs Bunny, Bugs chases after a shapeshifting villain, who on a building ledge disguises himself as a pigeon and sits among a group of pigeons. Bugs exposes the villain by scaring off the birds with a loud voice, getting them to fly off. The villain, realizing that he can't fly, ends up falling... though whether to his demise or not, nobody knows.
- Code Name: Gravedigger: In Men of War #21, Ulysses Hazard interrupts a Kill and Replace plot of the Nazis and finds himself confronted with two versions of his old friend Rupert Johnson. He quickly realises that the phony was the one who recognized him straight away. The real Rupert hesitated, because he had never seen Ulysses with the scar on his face he received while serving overseas.
- In the 2020 arc of Suicide Squad, Deadshot goes to find Ted Kord, the man who's been manipulating the Squad for some time. He's surprised to find Superman standing before a broken window with Kord bound and gagged. After they talk for a bit, Deadshot asks Superman to sign an autograph for his daughter. Once he does, Deadshot tells the Squad something is wrong: There's no glass from the window where Superman supposedly flew in, it's odd for Superman to tie and gag someone and the autograph says "to Zoe" when Deadshot never said who his daughter was. "Superman" is really Black Mask, having acquired a cloaking technology (which he's been using to impersonate Kord all this time).
- Black Mask uses it to impersonate Revolutionaries member Wink. Teammate Aerie instantly tells it's not her as Black Mask is about half a foot taller.
- Wonder Woman (1942): The Saturinans Sheika and Bandia impersonated Diana and Hippolyte to force the Amazons to declare war on the US, the originals escaped Saturnette's ship and called on the Amazons to tell the fakes from the true versions. The Amazons didn't have too hard a time, given that two of them were calling for war and to be an Amazon required women to take an oath declaring they wouldn't kill any humans.
- Dick Tracy has former actor Harley Naiv disfigured and given a surgery that turns his face into a malleable shape that can allow him to look like anyone. Taking on the name "Putty Puss," Naiv often faces Tracy but his impersonations can be spotted.
- To get money, Putty Puss poses as Diet Smith (who's running for President) for a speech where he makes outlandish statements guaranteed to ruin his campaign. Tracy, however, is able to use his 2-way wrist computer to record "Diet's" voice and while Naiv does a great impression, it still doesn't match Diet's distinctive voice pattern.
- Putty Puss tries to pass himself off as Tracy but Sam Catchem is able to catch it with one simple fact: "It'll be a snowy day in July before Dick Tracy wears anything but a checkered tie."
- Another time, Tracy is able to prove it's him simply by waiting as Putty Puss can only hold his face together for an hour before it starts to "melt."
- One week-long arc in Dilbert had the Pointy-Haired Boss abducted by aliens and replaced by a double. Everyone in the office immediately realizes this because the double is competent and possesses people skills. Due to the differences being good ones, they don't even try to save the real boss (who frees himself by accident when he teaches them Earth management techniques, causing the UFO to crash after the captain downsizes half the crew).
- In "The Two Brothers", collected by The Brothers Grimm, two identical twin brothers (with matching Loyal Animal Companions) set out to seek their fortunes; one has no particular luck, while the other rescues a princess from a dragon and marries her. When the brothers are reunited at the end, they decide for a laugh to go together to the court and not tell anyone which is which. Even the princess can't tell the men apart, but she identifies her husband after taking a close look at their animal companions. (Her husband's animals are wearing neck decorations she gave them after they helped kill the dragon.)
- In Seven Little Killers, Japan intends to shoot Canada for being one of the killers, but can't tell him apart from America; it winds up being a moot point since the gun isn't loaded, so he just flying tackles one of them into the river. To kick it up a notch, he does manage to drown Canada - it just turns out that he also mixed up which one was the real killer.
- In PnF: Stolen Identity, Ferb is replaced by a double for some unexplained but evil purpose. Said double spends the rest of the story acting so unlike Ferb that Phineas eventually thinks he's lost his mind and becomes completely terrified of his beloved stepbrother...meaning he fails this trope for most of the story. Fortunately he eventually figures out which is the real Ferb and the pair escape, leaving the evil double with the invention he needed Phineas to build for a reason we're never told.
- In Out of the Dead Land, this trope becomes a recurring plot element when evil robot duplicates begin attempting to replace the Avengers. Bucky is able to detect the robot-Sam impostor with his Super Senses and exploit the robots' lack of blood to test others whenever he gets paranoid or suspicious, but he does still get fooled by them at crucial times, most notably when Hydra shoots a Steve duplicate that was specially made to actually 'bleed' convincingly.
- In Doppelgänger, the Dark Doppelgangers have red eyes, which can distinguish them from their normal counterparts. However, Prussia has red eyes as well, making him identical to his. New Zealand solves this by punching them both in the face, as the doppelgangers have a nigh instant healing factor.
- In this My Little Pony: Friendship Is Magic fan comic, Shining Armor's put in this situation when Chrysalis changes into Cadance again. He asks Cadance to say Something Only They Would Say, which leads to an argument over Shining's obsession with a tabletop war game. When Chrysalis says that she loves that game, Shining grins at Cadance and says now he definitely doesn't know who to shoot, much to her horror.
- In the Doctor Who fic "Trial and Error", the Valeyard returns and attempts to take the TARDIS by claiming to Bill and Nardole that he's the newly-regenerated Twelfth Doctor, but Nardole sees through the deception as the Valeyard is wearing different clothes where a newly-regenerated Doctor would still be wearing his predecessor's clothing.
- In the Gargoyles fic "The Path Unfolding", recent attacks on Elisa appear to be the actions of a future version of Demona who came back in time using a time machine Xanatos created in the future. However, Elisa and Goliath each realise that the "future" Demona is a fake for emotional and tactical reasons; emotionally, Demona would never hire people to kill Elisa if she truly wanted Elisa dead when she could easily do it herself, and tactically Goliath knows that Demona isn't crazy enough to try and change history to achieve her goals when she already knows such a strategy wouldn't work.
- In the Quantum Leap/Star Trek: The Next Generation crossover "All That Glitters", Deanna Troi realises that something has changed about Data when she realises that she can sense him empathically, as well as a few more subtle details such as Data using contractions. When she confronts Data in private, she learns about Sams role in Project Quantum Leap and his likely reasons for being in the future, and basically acts as his Secret-Keeper to help him avoid making further slips.
- In "Ash's Adventure: Girls' Hunter Edition", Butch, Cassidy and James attempt to pose as police officers and arrest Ash, Misty and May while claiming they were responsible for a recent attack on the Viridian City Poke Centre, but others spot that the trio are fakes as their police car is using an outdated version of the Pewter City Police department logo which was abandoned when it was found to have a hidden penis in the sketch.
- In the Power Rangers Zeo fic "Memory Lapse", a monster tries to trick the Zeo Rangers' acquaintance Shawna by posing as Aisha, the ex-girlfriend Shawna still has trouble remembering, but Shawna swiftly realises the truth when "Aisha" can't catch a punch to her face as she recalls Aisha being a skilled martial artist who would have been able to catch the punch.
- Infinity Crisis: In Different Strokes, when the Earth-51 Deathstroke attacks the team, Diggle and Thea assume it's their Slade. However, Oliver says the fighting style is different and how he took this guy down with a move Slade himself taught Oliver. Felicity then shows video of how this Deathstroke is a few inches taller than Slade and his voice pattern doesn't match either.
- Deconstructed in A Prize for Three Empires. Mystique impersonates Carol Danvers and is spotted by Carol's lover Mike Barnett. Mystique proceeds to beat him to death.
- Defied in the Miraculous Ladybug fan comic Scarlet Lady. Just like in canon, an akuma takes on the appearance of Chat Noir to frame him for various criminal activities, and Scarlet Lady finds them duking it out in a warehouse. Unlike in canon, Scarlet Lady has a low opinion of her partner, was quickly willing to assume he turned to villainy because she thought he was jealous of her, and decides to just capture both Chat Noirs instead of figuring out which one's fake.
- This Bites!: During the attack on Marineford, Mr. 2 makes himself look like Cross in order to distract the Marines (who hate Cross more than they hate Luffy) and give Luffy a better chance of reaching Ace. However, Sengoku notes that Luffy isn't that concerned about "Cross" being attacked, despite the fact that concern for his True Companions is one of Luffy's defining characteristics. This allows Sengoku to determine that "Cross" is an imposter.
- Sev Trek: Pus in Boots (an Australian CGI spoof of Star Trek: The Next Generation). The crew find themselves confronted with two Captain Pinchhards, one of them a shapeshifting alien. Lt. Barf wants to kill them both, as the alien would revert to its natural state when dead, while Beta tries "statistical probability" ("eeny-meeny-miny-mo") but Commander Piker suggests asking a question only the real Captain would know.
Piker: Captain, what is my favorite trombone jazz number?
Pinchhard: How the hell should I know?!
Pinchhard 2: Beats me.
Piker: I played it for you on your birthday! You loved it!
Pinchhard: Oh please! I slept through the whole thing!
Pinchhard 2: Here's a combadge, Number One. Call someone who cares!
- Toy Story 2. When the toys realize they have two Buzz Lightyears, the real Buzz cleverly reveals his double's true identity by pressing the button that opens the double's bubble helmet. The double falls to the ground gasping for air, the same way the real Buzz did in the first movie. He clinches the identification by showing the toys the name "Andy" on the sole of his boot.
- Madagascar: Escape 2 Africa: Alex is forced to play this game when Marty blends in to a crowd of hundreds of zebras that look and sound exactly like Marty.
- X-Men Film Series
- X-Men has Mystique pulling that trick too. However, Wolverine can smell the difference between Mystique and Storm, so he doesn't fall for it. Later, Cyclops asks Wolverine to confirm he is the real thing:
Wolverine: You're a dick.
- In X2: X-Men United, the trope is averted when Stryker is able to recognize his "handiwork" on sight — it's enough to fool the soldiers, but somehow the Colonel can tell with one close-up look. Which actually isn't that surprising. Parents can tell the difference between identical twins even when others can't.
- X-Men has Mystique pulling that trick too. However, Wolverine can smell the difference between Mystique and Storm, so he doesn't fall for it. Later, Cyclops asks Wolverine to confirm he is the real thing:
- Done in The Island, with a twist: the impostor was the protagonist.
- Darkman did the same thing. His cover was blown, however, when his skin started melting.
- In keeping with the love that Star Trek: The Original Series had for this trope, it gets used again in Star Trek VI: The Undiscovered Country, at the climax of Kirk and McCoy's escape from Rura Penthe. A shapeshifter impersonates Captain Kirk, but it is the real Kirk the Klingons want to shoot. A "Shoot him he's the one" argument ensued, with an element of Fridge Logic: the shapeshifter should have tried to save herself by switching back to her normal form. She still would have been shot, but there's no explanation for why she doesn't. Fridge Logic kicks in when we consider the real Kirk still had his leg shackles on. The Chameloid morphed down to a little girl and had slipped out of them earlier. If you look at their feet during the "Kirk on Kirk" fight, you can see only one wearing them.
- In Duck Soup, when Rufus Firefly goes down to investigate, the Mirror Routine apparently goes off without a hitch, and then near the end, while Firefly and the disguised Chicolini are closely examining each other, Pinky disguised as Firefly comes into the doorway and blows their cover, and once Firefly sees the two impostors, Chicolini faces trial in Freedonia.
- Face/Off features a face-switch between the protagonist and antagonist, which both use to fool those close to their enemy. Hero Sean Archer convinces his wife of his true identity with the story of their first kiss.
- Terminator 2: Judgment Day:
- Page quote of Bluff the Impostor... and the closing fight scene where the shapeshifting Terminator has impersonated Sarah Connor, and John must work out which is the real one (which wants him alive) and the bad one (who wants him very very dead). He picks the good one.
- In the extended version, they reveal how John was able to make the right choice: due to the freezing/smashing/recombining the T-1000 went through, its morphing is damaged and it ends up copying the appearance of materials it is in contact with. John looked down and noted that the fake Sarah had a corrugated metal pattern on its legs. In another version, the heat rising through the grating below has melted her legs in the pattern of the grate.
- In Terminator Genisys, the T-1000 impersonates Kyle but when the real Kyle comes in, Sarah doesn't know whom to trust. She shoots one in the foot to see the reaction and it's the T-1000.
- Red Dawn (1984). One of the American guerilla fighters finds an U.S. Air Force officer who's been downed behind Soviet lines and asks "What's the capital of Texas?" When he replies "Austin" she replies that it's Houston and accuses him of being a Dirty Communist. Tanner replies that she's been watching too many movies. (Ironically Tanner gives the right answer, probably a Shout-Out to the incident with General Bradley at the Battle of the Bulge.)
- Happens twice in The Assignment (1997) about a US naval officer called on to impersonate Carlos the Jackal. On the first occasion, a terrorist who knows the real Carlos accidentally runs into the protagonist at the London airport. Unfortunately, the protagonist tries to bluff his way out by pretending to be Carlos, and when the terrorist responds, "I need to get a newspaper" realizes too late that it's a password to which he doesn't know the countersign. Later, his CIA handler mentions a similar incident where he was forced to kill a man who didn't respond with the correct countersign, and later uses this story to tell the difference between the protagonist and the real Carlos when he comes across them fighting each other.
- The blood test scene in The Thing (1982) qualifies. In fact, given the creature's ability to disguise itself, this is a constant theme of the entire film. If the blood test counts, so does any film or TV show that homages the blood test scene, such as The Faculty, with the drug test.
- Invasion U.S.A. (1952):
- A Russkie disguised as an American soldier doesn't know who the Chicago Cubs are ("Cubs? A cub is a small animal, a bear..."). Lampshaded by Tom Servo.
American soldier: Ever see the Cubs play?
Servo as the impostor: Yeah, they won... No! Damn!
- And later spoofed:
American patrol: Who goes there?
Crow, panicky: Uh, the Cubs! Studs Terkel! Saul Bellow! Oh, whatever, just shoot 'em!
- A Russkie disguised as an American soldier doesn't know who the Chicago Cubs are ("Cubs? A cub is a small animal, a bear..."). Lampshaded by Tom Servo.
- The climax of The Adventures of Pluto Nash involves the title character's fight against his evil clone and both wearing the same outfit. Pluto tricked the clone's goons into shooting the clone.
- Dragonball Evolution has this with Chi-Chi fighting against Mai shape-shifted into her. Goku fails to spot the imposter and punches out the real one, allowing Mai to escape.
- Police Academy 6: City Under Siege ends with the Big Bad posing as Commissioner Henry Hurst. To see who the fake one is, the police officers use the Pinocchio-test (they perform a nose pull on both commissioners, revealing the fake one is wearing a rubber mask).
- In Muppets Most Wanted, Miss Piggy manages to tell Kermit and Constantine apart by asking both of them if they'll marry her. Constantine just says yes while Kermit stammers in his answer, making Piggy realize that the latter is the real Kermit.
- In Enemy, Anthony's wife suspects briefly that Adam isn't her husband, but dismisses it. Adam's girlfriend, meanwhile, realizes who Anthony is leading to both of their deaths.
- In John Carter, an enemy shape-shifter turns into John and fools Tars Tarkus at first. When the real John arrives, Tarkus is confused at first but makes the right decision when he sees red blood dripping from John's wounds.
- The film version of Slaughterhouse-Five begins in World War II where soldier Billy Pilgrim wanders lost in the forest, and gets tackled by two American soldiers who think he's a German - they ask him who won the 1939 World Series. He doesn't know, and it turns out the other two don't know themselves.
- Ice Cold in Alex. The Main Characters begin to suspect that the South African officer who hitched a lift with them may be a German spy because he doesn't know how to brew up a Spot of Tea in the preferred method used by South African soldiers.
- In Captain Marvel (2019), this is used with Imposter Forgot One Detail to determine whether someone's a disguised Skrull:
Talos: Was it something I said?
- In the opening, Minn-Erva is aiming at some refugees when Att-Lass comes up to tell her they're okay. When Minn-Erva sees the real Att-Lass down on the ground, she realizes she's dealing with a Skrull.
- Fury and Coulson are chasing Carol, who's on a train chasing a Skrull. Fury doesn't believe in this crazy lady's story... until Coulson suddenly calls him from the site of the Blockbuster store, wondering where Fury went. Cue the Skrull in the car promptly attacking Fury.
- Fury makes it clear that everyone, even his own mother, only calls him by his last name. So when Talos, posing as Fury's boss Keller, calls him "Nicholas", he knows something's up. He then tells Talos about "doing a pincer move like in Havana." When Talos agrees to this mission that never happened (as Fury only has done missions in countries that start with the letter "B"), Fury's suspicions are confirmed.
- Yon-Rogg meets with Carol as they start questioning each other to see who's a Skrull. Carol is correct in that Yon-Rogg never tells anyone who the Supreme Intelligence appears to him as. But Yon-Rogg asks who gave Carol her Kree blood transfusion on Hala, and her pause makes him realize this is Norex, Talos's "science guy," distracting him from the real Carol. In this case, however, Carol actually gave her impostor the correct answers, so either she didn't realize Yon-Rogg would get so detailed, or Norex blanked under pressure.
- In Seven (1979), Drew is able to tell that the first figure he sees on the Kahuna's boat isn't the real Kahuna, because the real Kahuna is left-handed.
- The One: In the end, the Multiverse Authority is faced with Gabe Law and his evil doppelganger Yulaw who are wearing the same outfit. Funsch figures out Gabe has a tan line from his discarded wedding ring which Yulaw lacks since he was never married.
- Attempted by Gordon in Wild Wild West to save Ulysses S. Grant from Loveless, when he dresses up as the general and tries to pretend he is the real one while "Grant" is an imposter. Loveless doesn't even blink and just captures them both.
- Alex Rider:
- Point Blanc ends with a genuinely disturbing sequence in which Alex and a clone of the BigBad surgically altered to look exactly like Alex go mano a mano. The prose deliberately acts like a distant camera, leaving the reader to play Spot The Doppelgänger and find it impossible, even when one falls into an inferno. In the next book, everything's all fine and dandy with Alex being the survivor, but...
- Pops up again in Scorpia Rising: the clone (who survived the fall) and Alex are pointing guns at each other, and a CIA agent who comes on scene has to determine which of them just tried to assassinate the American Secretary of State. He makes a correct deduction (Alex had a pistol, but the clone had a rifle, a sniper's weapon) but is shot before he can fire his own gun.
- In the Thursday Next book First Among Sequels, Thursday fights off a fictional duplicate of herself. As a twist the writing changes so that we see things from the duplicate's point of view, despite being in the first person narrative, and without warning. It can take a reader a while to notice the switch.
- Meg must perform this task in Madeleine L'Engle's A Wind in the Door, distinguishing her detested principal Mr. Jenkins from two imposters created by echthroi (which are essentially that universe's equivalent of demons). The imposters try too hard to be Mr. Jenkins and so fail, while the real Mr. Jenkins simply acts like himself (bored, confused, and wondering when this little game will be over).
- Averted in Brothers in Arms by Lois McMaster Bujold. Miles is kidnapped, replaced by his clone, and interrogated; at one point in the interrogation, he and the clone are briefly alone together. He considers trying to trick his captors into thinking that he's the clone, but rejects the idea when he realizes that he hasn't shaved since he was taken and is currently sporting several days more stubble than the clone is.
- The Iron Man novel Operation: A.I.M. had several Avengers battling shapeshifting "adaptoids"; Iron Man tricks the War Machine impostor into giving himself away by pretending his Powered Armor had a chameleon circuit. When the android uses this as an excuse to shapeshift in front of the others, his cover is blown two of the three other heroes there, Captain America and the Black Panther, were also adaptoids. Iron Man was at that point on his own but hadn't realized it yet. Later, the heroes must fight their own doppelgangers and resort to uncharacteristic tactics to win since the fakes know all their usual moves.
- In the online novel John Dies at the End, determining who is a copy is simple, since their makers actually mark each clone's big toe. This leads to a Tomato in the Mirror for one of the Main Characters.
- Subverted in Maximum Ride. After the situation is set up, the imposter is instantly identified by Angel, who points out "I can read minds, you moron."
- In the David trilogy, David morphs Jake's cousin, who is badly injured after being hit by a car and expected to die in surgery, and takes his place. Jake figures it out almost instantly, when "Saddler's" injuries are miraculously healed. Everyone else not in on the masquerade fails miserably.
- David also impersonates Marco. When a Marco shows up, he's tested by the others: they make comments to him and see if he responds sarcastically.
- A one-man variation in #6 when Jake gets infested by a Yeerk. The Yeerk is unable to contain its hatred of Andalites, and blows its cover for good when it protests being tied up for three days (the maximum duration Yeerks can survive without soaking up Kandrona rays), which the real Jake would instantly have agreed to.
- It also gets some time in the Harry Potter books because of the Polyjuice Potion: at the start of Order of the Phoenix, where Lupin asks Harry what his Patronus is, several uses after the Seven Potters escape, and a number for trying to detect Death Eater impersonators.
- Clive Cussler is fond of this in several of his books. Indeed the Dirk Pitt novel Iceberg has several examples:
- Pitt is recovering from a plane crash in Iceland with a local doctor when a pair of cops stop by to ask questions. They state they just had coffee with the sergeant of a local village before he went on patrol. In private, the doctor tells Pitt the men are imposters as that sergeant doesn't patrol the area and is allergic to coffee. Pitt had already noticed one of the "cops" had patches on his shoulders where a sergeant's stripes would be.
- Pitt meets with Kristi Frye, the long-hidden sister of the late explorer/researcher Kristjan Frye. Pitt is stunned when later in the book, it's revealed that Kristi is Kristjan, having undergone a sex change to be the woman she's also longed to be. While he didn't expect that, Pitt does find something off and over dinner, talks of how, in New Guinea, he ordered an echidna seaweed and Kristi agrees it's a great dish. An odd reaction given how Pitt just said he had the equivalent of "a New York cut steak wrapped in porcupine quills."
- Asked how he knew something was wrong, Pitt explains that Kristi's tan was far too shallow for someone who was supposed to have spent years living in the South American jungle.
- In the novel's climax, Pitt rescues a pair of diplomats from assassins on the Pirates of the Caribbean ride at Disneyland. Asked how he knew the killers were posing as robot pirates, Pitt quotes Walt Disney himself on "we were eyeball to eyeball and I saw the other fella blink."
- Stay Out of the Basement involves a plant clone. After the clone is revealed to be a plant being, the plot seems to wrap up... until a flower in the front garden attempts to convince the protagonist that it is the real one.
- In I Am Your Evil Twin, the protagonist uses his food allergy to prove that he's not the evil clone. Unfortunately, the clone swaps the target food for a version the protagonist is not allergic to, and then vomits on purpose, successfully fooling everyone into thinking he's the real thing.
- Spoofed in The Culture novel Matter when Upper-Class Twit Prince Ferbin is on the run and seeks help from a former tutor who, to verify his identity, asks him a series of questions from his studies. When he gets them all wrong, the tutor responds dryly that Ferbin is indeed his indifferent student from long ago.
- Played with in the Phule's Company book Phule me Twice, in which the identical looking robot is never recognized, despite its limited programmed responses, which are all casino based. Even the Company smart folk don't get suspicious when advised to try the slots or the all-night buffet. Instead, they fear sunstroke. After Phules' return, they use the robot to drive the unwanted new CO over the edge, as he wouldn't know about its existence.
- In Sewer, Gas & Electric, Harry Gant is kidnapped and forced to compete against his robot duplicate in a video game, with his parents' lives as the stakes. His ex-wife breaks in to rescue the Gants, and the robot tries to trick her by voicing its "relief" at being "saved". She immediately shoots the robot, knowing that the real Harry is such a game addict that he wouldn't even notice her arrival.
- God-Emperor of Dune inverts this, where there's an army of impostors and the task is to spot the real one. Leto II's Fish speaker army is facing a legion of shapeshifting Face Dancers who are impersonating his general, Duncan Idaho. When he scans the crowd, he immediately spots a naked one among the copies.
- In a Nancy Drew book, when referring to a man who had been hospitalized, another man says, "taken to hospital", instead of "taken to the hospital". The former is a British term. The man has been posing as an American to escape crimes he was charged for in England.
- At least two examples in Journey to the West:
- In chapter 39, a demon disguises himself as the Tang Monk. Sun Wukong chases down both him and the real Tang Monk, but can't tell them apart. In an inversion of Kill Us Both, Sun Wukong asks both monks to recite the spell that will tighten the crown on the Monkey King's head. Knowing he can't do it, the imposter flees.
- Later, when two identical monkeys claim to be the Monkey King, and they take their fight to continuously more powerful divine beings, all of whom (except the last) fail to identify the real one. This one is solved via Deus ex Machina.
- Subverted in A Farewell to Arms by Ernest Hemingway. The protagonist (an American volunteer in the Italian army) is arrested as a German infiltrator because he speaks Italian with an accent—as does the military policeman arresting him (as he points out to no avail) as most Italians were more familiar with their local dialect.
- Partially subverted in the first story in Isaac Asimov's The Union Club Mysteries, where a club member named Griswold commented that spies sent to infiltrate defense agencies in particular were recruited from among people who'd spent several years in the US and were thoroughly grounded in American trivia. He then told of how he'd unmasked one such spy whom he'd been interrogating for hours by playing a word-association game which finished with him saying "terror of flight" and the spy responding "gloom of the grave." This was a giveaway because both phrases are from the third stanza of "The Star-Spangled Banner," and "...no loyal, true-blue American knows the words of the third stanza of our glorious national anthem" making it much more likely that it was a spy who had studied too hard.
- In one of the Clue mystery series stories, Professor Plum makes several clones of Miss Peacock, alike in every way, save that the clone-Peacocks always lie. They corner all of them, all acting like fuss-budgets, all claiming to be the real Peacock, and the reader is asked how to tell them apart. The answer is to ask any simple question with a non-subjective answer, like "What is 2+2?".
- Implied to happen offscreen in The Dresden Files, and rather frequently, at that. Ghost Story, covers how Chicago has gotten a great deal Darker and Edgier since the events of the previous book, Changes, six months previous. In order to verify a character's identity, Karrin Murphy demands that he "Bleed for me." Not only does he do so without protest, he has a pin on him for such a purpose. Harry notes that, while there are a great many supernatural shapeshifters, none of them can create convincing blood. He also comments on how bad things must have gotten in the six months he's been dead for the test to have gotten so commonplace.
- The short story "Granny Gumption Solves a Murder" has the title character, a little old lady turned amateur sleuth, confronting the supposed returned son of a wealthy family. She knows he's the murderer who killed a doctor who was seeing through the ruse and says the tip-off was that his well-manicured hands don't match "the prodigal son who spent ten years working in the Peruvian mines," indicating he's an imposter. She urges him to turn himself in but he has other ideas.
- Galaxy of Fear:
- The Nightmare Machine has an elaborate and convincing simulation going on in which the Main Characters' worst fears are realized. Zak realizes that his robot caretaker DV-9 is actually a sim because Deevee never reacted to the simulations before, among other things.
- In Clones, the original and clone Hooles had fought a Shapeshifter Showdown; Tash had been watching, both because it was fascinating and because she didn't want to have to do this trope when they were done, but is interrupted and loses track. Soon she does have to spot which one is real... and comes up with something.
"There's no way to tell you apart," she said, raising the blaster. "I'll just have to shoot you both."
Tash shrugged. "Clones don't really understand feelings that well. The real Hoole would have known I couldn't shoot him, but the clone wouldn't know that. I knew he would believe my threat, and try to stop me."
- The clone jumps at her, so she blasts him. The real Hoole asks how she knew.
- Earlier in that book a clone of Zak wants Tash to enter a code, but she stops warily, thinking that he's supposed to know the code too, and why wouldn't he have done it himself? These clones have many of the same memories as their templates, but apparently in less detail.
- In the story "The Brain Stealers of Mars", the thushol are Martian shapeshifting parasites who impersonate the heroes. They're also mind-readers, so that a duplicate has all the knowledge of the original, and the heroes can't find out who is the real one by questioning each other.
- In the early story Counterfeit, an alien imposter who has infiltrated the crew is detected in a medical check because the imitation isn't quite perfect; amongst other faults, the alien has a blood-glucose level of zero — a real human would be dead.
- In the Star Trek: The Next Generation novel "Rogue Saucer", Picard and his bridge crew, flying the stardrive section of the Enterprise, are confronted by two saucers — the Enterprise's own, and the rogue of the title. Picard and Worf quickly work out the solution: open fire on both. The one that fires back is the rogue.
- The point of the story in Emily the Strange: Stranger and Stranger. The two Emilys are trying to determine which one is the real one.
- The plot of The Tightrope Men by Desmond Bagley involves a man who has been altered by plastic surgery to resemble a Kidnapped Scientist. He gets a nasty shock when the man's daughter turns up for an unexpected visit, but is able to bluff things out for a while with the help of his government minders, until the day she informs him that she just spend the past hour testing him with a Long List of trick questions because she's tumbled to the fact that he's an imposter.
- The central conceit of Who?, a short story and later a novel by Algis Budrys (made into a movie in 1974). An American scientist is injured in an explosion, and abducted by the Soviets in the guise of giving medical treatment which involves turning him into a cyborg. When political pressure forces the Soviets to return him, the Americans face the possibility that a spy could have been sent in his place — his face is now a metal plate with vision slit, he has a metal arm and the other could have been transplanted from the Kidnapped Scientist. In the short story a simple ruse reveals he's genuine, but in the novel the scientist is never cleared of suspicion and has an existential crisis thanks to this and his injuries.
- The Innsmouth Legacy. In Deep Roots, FBI agent Ron Spector has been replaced by a doppelganger, a fact that the Irregulars realize only because he's Distracted by the Sexy when he's actually a closet homosexual. Unfortunately, when they bring the imposter to his colleagues (being unable to reveal how they exposed him), he's able to pass their Something Only They Would Say questions because he has all the memories of the real Spector, having been copied from his mind.
- In Mistborn, Kandra can take the shape of anyone, as long as they have their skeleton. When Vin and Elend discover that someone in the castle has been replaced by a kandra, they are given some clues from their own kandra: they need to interrogate their captives first, they can't use Allomancy, and they aren't affected by Emotional Allomancy. Vin spends some time screening her fellow crewmates by putting them in situations where they'd use Allomancy, but has to question Dox on a conversation they'd had a few years ago.
- Later, a soldier confirms Vin's identity by asking a trivial question they both know, but a kandra wouldn't ask: what did she have for dinner last night? Eggs.
- The Bible makes this Older Than Feudalism. From 1 Kings 3:16-28, King Solomon was famous for his wisdom, not only because he prayed for it, but because he was able to figure out which of two women was the mother of a child (a trope of its own). One woman's baby boy was dead, and both women claimed to be the mother of the living baby. He spotted the imposter when he offered to take a sword and cut the baby in half, allowing each woman to have a half of the child. The woman who gave up her claim rather than let the baby be killed was judged to be the true mother. Also likely the origin of the "kill both of us" gambit, though that is a variation.
- Parodied in the first arc of The Adventure Zone: Balance. Magic Brian assumes the form of Gundren Rockseeker, but his heavy accent gives him away immediately and he's utterly oblivious. Here's a fan animation of the scene in question.
Magic Brian: Oh noooooooo, the mystery is solved! Youve solved my final riddle, you are ze new riddle master-![the other hosts (and probably their characters) are in stitches]
- The infamous nWo Sting angle in WCW where the nWo introduced an impostor Sting around the same time the real Sting had changed his look, meaning no one recognized him at first.
- The infamous Dragon Door Project, whose main angle revolved around a half dozen wrestlers impersonating Último Dragón or Tiger Mask, along with a Tiger Dragon.
- During the "Pikachu!" number in Pokémon Live!, Jessie and James are hampered when multiple Pikachu appear, forcing them to pick out Ash's from a crowd.
- Among Us is practically built around this trope, as the main goal of the players is to find out which ones of them are Impostors who seek to kill every Crewmate who isn't an Impostor onboard.
- The Spy in Team Fortress 2 turns every game into one of these. You can't really be sure if that guy on your team is actually on your team, or if he's just waiting to stick a knife in your guts. Or more likely, it turns every game into a case of "Kill 'em all, let the friendly fire system sort it out!" But servers with friendly fire enabled do play this trope straight, breaking spies in the process.
- Spoofed during Chapter 7 in Paper Mario 64, where several duplighosts (ghosts that can duplicate your appearance and abilities) impersonate your partner. The first two encounters are played more-or-less straight, but in the third, the four duplighosts trying to duplicate Kooper the Koopa end up looking and talking like several different characters, including Luigi, while still claiming to be Kooper. The one that impersonates Luigi even claims that you should trust him to be the real Kooper because you should trust your brother.
- Done again in Super Paper Mario, where Mimi impersonates Merlee. You go through a quiz game imitation to determine which one is the real one. The real way you tell them apart is by the fly hanging around the real Merlee - she was hiding in a toilet just before this incident. It's also possible to tell by the way they speak - Merlee's rhymes and rhythm are perfect, but Mimi's are subtly inconsistent and are about nasty and evil things.
- In King's Quest VII: The Princeless Bride, near the end, the impostor king and real king fight each other as the hero stands by with a wand which can change the impostor back to his true form.
- In The Legend of Heroes: Trails of Cold Steel II, a side-mission involves Phantom Thief Bleublanc; an antagonist from The Legend of Heroes: Trails in the Sky, sneaking onboard The Courageous and impersonating one of the members of Class VII. He challenges Rean and the others to find out which person he's disguised as, also to see how strong their trust is to each other.
- In Viewtiful Joe 2, right after defeating Frost Tiger, Joe finds two Sylvias, both claiming that the other is an impostor after the Rainbow Oscars. Being an Idiot Hero, Joe falls for the feminine wiles of the android impostor, even after Sylvia names the food they had on their first date.
- In Granblue Fantasy, a chapter in the "Detective Barawa: The Jewel Resort Incident" event requires the player to choose who the imposter is among the 3 NPCs... by hitting them with their weapon. Chat Noir disguises himself as Therese in a bunny outfit.
- Parodied at the end of No Time to Explain, as The Guy is battling his Evil Clone, two of his future selves have trouble identifying which one is clone despite having seen the clone's face multiple times.
- At one point in Hamtaro: Ham-Ham Heartbreak, Spat first masquerades as Pashmina and coldly rips Penelope's blanket, then masquerades as Penelope and jumps all over Pashmina's scarf, causing Penelope and Pashmina to each think the other one is angry with them. Eventually, Spat settles on masquerading as Pashmina. How does this predicament get solved? The same way Solomon solved the riddle of the two mothers: Hamtaro and Bijou propose that both Pashminas tug really hard on Penelope... which hurts Penelope, so the real Pashmina is the one who lets go first to stop hurting her.
- In Tales of Symphonia: Dawn of the New World, Emil comes upon two Lloyds fighting each other. Even if you never played the original, it's still pretty easy to figure out which one is the Lloyd responsible for all the atrocities in the world — he's the one spouting the cliched lines about justice and bouncing on the balls of his feet with a giddy expression. The actual tell (In-universe) is the Impostor tries to invoke "For Great Justice!!!!", something that was a major peeve for Lloyd back in Tales of Symphonia.
- Averted in Fire Emblem: Radiant Dawn. Pelleas, the alleged son of King Ashnard, hardly resembles Ashnard's real son at all, except for a mark on his forehead. In fact, the identity of Ashnard's real son is essentially irrelevant to the story.
- In Metal Gear Ac!d, Teliko gets doubled by La Clown and they have a game of this with Snake. Her cover is only blown when the game begins again and the player (controlling both Snake and Teliko) gets a turn as Teliko.
- There's also one in Metal Gear Solid Mobile, when Snake starts receiving Codec calls from a mysterious figure. This figure later claims to be Otacon. But Snake is being helped by Otacon already, and he knows nothing about the other person — and can't even detect their Codec calls. It's later revealed that the interloper is the real Otacon. The Otacon helping Snake is an AI based on Otacon's personality in the hellish VR simulation Snake has been put into.
- In the fourth episode of Strong Bad's Cool Game for Attractive People, "Dangeresque 3: The Criminal Projective", Dangeresque is forced to choose between shooting his partner Dangeresque Too or the criminal lookalike Uzi Bazooka. Whichever you pick as the player, though, Uzi Bazooka is the one who gets shot.
- Live A Live has the player stuck in the "Prove yourself" half of this in Cube's chapter. When faced with both Cube and a hostile robot modeled after him, Kato muses aloud that since the fake was only activated a short time ago, he couldn't have heard Kato's first idea for Cube's name (Koro or Rover, depending on your translation; either way, it's a cliché dog name). When you give the right answer, Kato yells for Darth to shoot the other one.
- In Animal Crossing: New Leaf, on April Fool's Day, Blanca will arrive in your town, and visit a random neighbor. You have to guess who the real neighbor is; Choosing the actual neighbor instead of Blanca nets you a reward from your neighbor.
- In Who is Mike?, the titular Mike comes face-to-face with a mysterious duplicate with the same memories and personality as him, and his girlfriend Sarah has to decide which one of them is the real Mike. There's also a story branch in which Mike has to choose between two Sarahs after the fake Mike impersonates her.
- The final level of Fear Effect 2: Retro Helix has Hana being forced to identify which is Rain and which is Mist, with the choice determining the ending to the game. It's the one holding the disk — Rain's left handed.
- A variant happens in Hyperdimension Neptunia Re;Birth1. Financier knows which identical copy of Blanc is the real one, but has to publicly prove it so Blanc gets her shares back. Her solution is to bring both Blancs to the town square and quiz them on her fanfiction. One copy answers the questions perfectly. The other gets defensive, avoids giving straight answers, and then starts loudly swearing at everyone present. The people instantly recognize the genuine article's short fuse, colorful vocabulary, and embarrassing hobbies.
- In Treasure Planet: Battle at Procyon this happens in Mission 11, where the player encounters two ships claiming to be commanded by John Silver, and must work out which is the real one and shoot the imposter.
- In Detroit: Become Human near the end of the game, if Connor goes to the CyberLife Tower and attempts to activate the androids in the warehouse, another Connor will appear, holding Hank hostage. A tense standoff will occur where the two fight and Connor must convince Hank he is the real Connor, after Hank aims at them both. Hank tell the Connors to tell him his dog's and son's name. Since the fake Connor has all of Connor's memories, he isn't looking for the correct answer but the more empathic one.
- The Jackbox Party Pack
- Party Pack 3 has the game "Fakin' It", where all the players get a series of prompts on their device they must follow... except for a "Faker" whom the other players have to identify before the game is over.
- Party Pack 6 has "Push The Button!", a Mafia/Werewolf-like game where a group of astronauts are in a Race Against the Clock to find out who among them is a shape-shifting alien. They do this by subjecting their fellow crew members to a series of questions and tests. The aliens must try to blend in, despite getting a different prompt from the humans during each challenge.
- Occurs in Threads of Fate during Mint's story, where a doppelganger is impersonating her sister, Maya. The player is given the option to pick which one to attack after speaking to both. Subversion, since Mint is a Jerkass and makes a wild guess. Regardless of whether you choose correctly, the sisters then double-team the exposed imposter.
Mode Master: How did you see through my perfect disguise?
Mint: It was just a wild guess.
Mode Master: !!!?
Mint: What's the big deal? If I was wrong, I'd just end up kicking both of you.
- Happens in Yakuza: Like a Dragon, when Adachi gets wrangled into a struggle with Mirror Face, an assassin disguised as him. Since Adachi worked at the DMV, Ichiban decides to quiz them on traffic laws, with one answering accurately and the other being utterly baffled by them. Ichiban proceeds to punch out the one who answers accurately, leading to Mirror Face lying on the ground wondering how someone like Adachi even kept his job in the first place.
- Seen in the fourth Detectives United game, when Agent Brown is on a secret mission to stop his Evil Twin brother. Naturally, his friends have a little trouble figuring out which of them is the real Agent Brown; however, this example is a bit more complicated than most, since both twins are invisible.
- In episode 3 of The Council, Luis is caught in the middle of a violent confrontation between twin sisters Emily and Emma Hillsborrow. The two sisters both live publicly under Emily's identity, which has made Emma resentful and unstable over the years. The player then has to ask them questions to deduce who's the "real" Emily, which is easier said than done since they always share information to keep up the ruse. To complicate things even further, Luis may have slept with one or both of the sisters at different points, and it's not clear at first who was "playing" Emily at the time. No matter who you choose, the chosen sister will always kill the other one and you won't find out if you were correct until the next episode.
- Your Turn to Die has this as the crux of one of its deadly games — though the participants aren't aware of it at first. One of their number has been secretly replaced by a Doll, and the only way to avoid one of them dying is to identify and sacrifice the fake instead. Naturally, this is made much harder by the fact that the Doll isn't aware of their own status, and is technically innocent in all of this...
- Red vs. Blue Revelations:
- Parodied when a newly revived Tex is fighting the rest of the soldiers. At one point, Tucker's armor gets turned black (like Tex's) and Tex starts pummeling him.
Simmons: They look the same! Which one do I shoot?!
Tucker: Ow! Shoot the one who's winning, dumbass!
- Played straight in Season 15, where Simmons ends up in a scuffle with his Evil Counterpart, Gene, who happens to look and sound exactly like him. Grif solves it with the classic "Why are we here?" gag.
- Parodied when a newly revived Tex is fighting the rest of the soldiers. At one point, Tucker's armor gets turned black (like Tex's) and Tex starts pummeling him.
- Rocket & Groot: When chasing after a shapeshifter, their target turns into Rocket. Unable to tell the two apart, Groot grabs them both and questions them. The find Rocket tells him how much he cares for Groot, and the other one angrily demands Groot to let him out immediately. Groot figures out the real one quickly.
- Played straight in The Gmod Idiot Box. Louis is trying to decide which Francis is real (one is a spy). He tells them to go up stairs. The one that gladly does gets shot. It then gets parodied the next moment, when Louis decides that they have to go up the stairs, and the real Francis hates stairs, so he shoots Louis.
- Dorkly Originals: This Sonic Parody video has Tails initially confused which one is the real deal between Sonic and Metal Sonic despite the fact that Metal Sonic constantly gets facts wrong, can't even talk correctly, and doesn't remotely look like Sonic aside from being blue, which Sonic lampshades. Tails does manage to quickly shoot Metal Sonic, but in a subversion the shot ricochets and ends up killing the real Sonic anyway.
Mecha Sonic: Way to kill that fake, phony imposter, Trails the Hedgefund.
- The Misadventures of R2 and Miku: When faced with 10 Miku clones, R2's immediate reaction is to pull out a gun and invoke this trope.
- Pico vs. Convict culminates with Pico being forced to shoot one of two Nenes, one of which is actually the shapeshifting Serial Killer Convict. He chooses incorrectly.
- Webcomic parody in this strip of Lil' Formers, in which the customer falls for a blatant knockoff. And again in this one, in which both of the imposters are extremely incompetent.
- The Order of the Stick:
- The "You'll have to shoot us both!" subversion gets double-subverted as well as heavily lampshaded (even going so far as to call it a "trope") through lack of Genre Blindness on this page. Of course, this comic also shows that spotting the impostor is easy when he has an ego the size of the Tarrasque.
- During the Azure City War arc the Order can see three different figures who look like Xykon—two fighting, one hanging back on the enemy side—and have to figure out which the real one so they can stop him from getting to the Gate. Haley eventually figures out that it's none of them—after all, if he can make two decoys why not three? Then they realize the real Xykon is invisible, flying right above them on a similarly invisible zombie dragon.
- Durkon states that the second hardest thing about being vampirified and trapped inside his own mind while the vampire itself puppeteered his body was learning that only Belkar could tell the difference between him and an evil spirit.
Elan: In my defense, I am not very smart.
- The Stick-Figure Comic Stickman and Cube does this during the "Cube Disappears" arc. After Cube disproves his own existence, Stickman builds a robot duplicate called Robo-Cube as a temporary replacement. However, after the real Cube returns, Robo-Cube impersonates him.
Stickman: See, this is why you never, ever build exact robot duplicates of people.
- Planet Zebeth has a sequence in which Samus fight against a backup copy of herself from a save file, and during the battle the scene cut away to other characters watching, so there is no way to tell who won. (However, the two characters are clearly not completely identical — they've experienced different things, so if there's ever a situation in which the differences come up we will know!)
- Khrima, the main villain of Adventurers! made robot copies of the whole heroic party to replace them with, in one strip. The plan fell through since, after all, what's the point of replacing the WHOLE heroic group? He even made a robot copy of Spybot, who was a robot (and supposedly working for Khrima anyway).
- Gets time in Sacred Pie starting in this strip.
- Saturday Morning Breakfast Cereal
- Played with here.
Silently, we both wondered who the hell she was [and why she was trying to decide which one of us to shoot].
- And here. She chooses the imposter. Same thing for different reasons here.
- The strip "Mom" suggests that faking this trope to your kid for the hell of it is the best possible use of a long-lost twin.
- Played with here.
- Subverted with Molly and Golly in the first panel of this strip from The Inexplicable Adventures of Bob!.
- Amazing Super Powers:
- Subverted in Dead of Summer. The deal with Panther and his clone seems to be leading into this, as the two meet face to face...and the real Panther takes the clone out in one blow.
- Subverted in this Cyanide & Happiness.
Evil Jim: He was the real one.
Gun Holder: I know.
- In The Dragon Doctors, one thief disguises herself with an identity-theft spell to escape a failed robbery — and even warns the people she's trying to fool that she's impersonating someone to escape.
- Bob and George:
- In El Goonish Shive, Tedd faces a 'Which Grace is real?' dilemma, but quickly figures it out.
- One Phuzzy Comics update had the third party responsible for spotting the imposter be the cat.
- In TwoKinds, the gang is trying to figure out whether or not the summoned shade of Laura is really her spirit (as Keith thinks) or a magic construct based on Keith's memories (as Natani, who cast the spell, states). Trace asks "Laura" about the first time he and Laura met. "Laura" protests that Keith was there, so that doesn't prove anything. Only Trace and the real Laura would know that that incident was the second time they'd met.
- During a fight scene in Archipelago, Face-Changer Han impersonates Riley in front of his twin brother. Subverted when Tuff gives his brother's BFS to Han instead of Riley; double-subverted when it turns out that Han couldn't copy the strength required to carry said sword, which is what Tuff was banking on. He already figured out who was who beforehand— the real Riley's pants were unbuttoned at the time, which Han failed to notice.
- Subverted in Skin Horse. Baron Mistycorn agonizes over which Nick to shoot... completely ignoring that the duplicate has willingly identified himself.
- The Handbook of Heroes comic "Doppelganger" has Fighter resolving one of these dilemmas by simply killing both — after all, they can just resurrect the real one later.
- Satirised in "Quick Solution" by Wordpress user Gato Gordito; a boy having to decide which of his mothers is a robot imposter solves the issue by playing the Xbox 360. His real mother mistakes it for Nintendo, so he shoots the robot imposter, who identifies it as a Xbox 360.
- In the Narbonic storyline "Professor Madblood and the Doppelganger Gambit", Dave is transmogrified into Madblood to infiltrate his moonbase, and then hides amongst Madblood's robot duplicates when the real Madblood returns. Madblood decides to flush out the imposter by making the androids sing the "Madblood Battle Anthem", since the imposter wouldn't know that. However, the androids don't know it either, so Madblood teaches it to them. This turns out to work anyway because Dave is so enthusiastic about singing it. Later in the same storyline, Madblood uses the transmogrifier to pose as Dave. While he's completely unconvincing when he contacts Helen, Mell is confused when she sees two Daves fighting over cigarettes, and it doesn't help that Artie, having been sent to the Moon in a faulty teleporter, now also looks like Dave.
Mell: But how can I tell which one is the real Dave?
Artie: The one without the flannel is the evil imposter! Punch him!
Mell punches Artie
Artie: Let's try again: I'm the good imposter. Don't punch me.
Mell: That's what they all say.
- An early episode of AH.com: The Series has a Shout-Out to the Red Dwarf example above, when the crew pick the real Doctor What from his Mirror Universe Evil Counterpart by rapid-firing questions about Paris Hilton at him. Later referenced when a different Evil Counterpart's deputy tries to use it, but the real Doctor What quickly shouts out the "right" answer and thus she picks the wrong one.
- Whateley Universe story "Test Tube Babies": Flying Brick Lancer fights power mimic Duplikat. Shroud finds herself facing two identical Lancers. One even tells her to shoot both of them to be sure. The team has a secret comm system so Shroud knows which one is the real Lancer.
- In 80's Dan, Mr. Crabtree wanted to shoot whoever was the fake Dolly (even though the fake looked nothing like the real Dolly, and was a guy), not because the fake Dolly was dangerous, but because Mr. Crabtree just needed to let off some of his stress.
- One of their shorts involves the game with identical copies of Elizabeth Mitchell. Played with, as it's obvious from the start who the copy is, but the player is hoping to get laid, and the original isn't putting out.
- An article on the site featured this in a Gamebook format, with a woman torn between shooting two identical-looking versions of her husband.
- If you shoot the one with the green shirt, both the remaining guy AND the girl are revealed to be aliens.
- If you shoot the one with the yellow shirt, you killed the alien impostor.
- And if you shoot neither, the woman instead suggests a threesome between herself, her husband, and the alien clone, which is then revealed to be just a nightmare that the real husband was having.
- Parodied by Nigahiga when Ryan has his Evil Twin and one of his friends at gunpoint...and can't figure out who the real Ryan is.
- Taken to the next level by Karl on The Ricky Gervais Show, whose stupidity was such that he did not like the idea of having a clone on the basis that he wouldn't know which one he was.
- In the SuperMarioLogan episode, "Jeffy Sneaks Out!", Mario grounds Jeffy from going to the movies with Bowser Junior for repeatedly saying the F word, so Jeffy creates a clone of him from his Play-Doh (It Makes Sense in Context) to take his place while he sneaks out. Play-Doh Jeffy causes havoc at Mario's house, and towards the end of the episode, the real Jeffy gets into a fight with Play-Doh Jeffy, and Mario gets a hold of officer Brooklyn T. Guy's gun, with intent to shoot the Jeffy impostor. Despite the two Jeffys looking nothing alike, Mario and Rosalina are unable to tell them apart. At first, Mario sings "The Bunny Do", but both Jeffys dance along to it. He then grounds both Jeffys, and the real Jeffy goes into a swearing fit, prompting Mario to shoot Play-Doh Jeffy.
- At the start of the Sanders Sides video, "Selfishness v. Selflessness", Logan pops up to give his input on the situation at hand (Thomas is torn between going to a friend's wedding or a callback for a movie role) and saying if Thomas doesn't want to go, they should "hear it straight from the horse's mouth" and then says "Thomas, the floor is yours". This immediately clues in Thomas and the other sides that it's actually Janus impersonating Logan since the latter is incapable of understanding or using most idioms.
- ClickHole: In "Incredible! We Asked These Astronauts What It's Like To Be In Space", most of the fictional astronauts' replies are completely inane, but Barry Wilmore's quickly turns disturbing:
You never know true beauty until you see Earth from space, or true terror until you hear someone knocking on the space station door from outside. You look through the porthole and see an astronaut, but all your crew is inside and accounted for. You use the comm to ask who it is and he says he's Ramirez returning from a repair mission, but Ramirez is sitting right next to you in the command module and he's just as confused as you are. When you tell the guy this over the radio he starts banging on the door louder and harder, begging you to let him in, saying he's the real Ramirez. Meanwhile, the Ramirez inside with you is pleading to keep the airlock shut. It really puts life on Earth into perspective.
- Woolie once went against his Evil Counterpart, GreatBlackOtaku, which ended when Matt shot Woolie dead, either believing GBO to be the real Woolie or pretending to think so to get on his good side.
- Boston landmark Faneuil Hall has an unusually shaped weathervane (a grasshopper), which was sometimes used as a Spot the Impostor test during the American Revolutionary War.
- Alan Turing proposed that a computer program which could win a text-only game of Spot the Imposter should be considered intelligent. The "Turing Test", as it's called, is a popular challenge for A.I. programmers to try to overcome, though it isn't seriously considered a benchmark for true intelligence in a computer. The original paper is available online, for the curious.
- During the Battle of the Bulge, German troops in US Army uniform infiltrated the lines with the intent of causing sabotage and disruption. Checkpoints grilled GIs on things every true-blooded American was expected to know such as the identity of Mickey Mouse's girlfriend, baseball scores, or the capital of Illinois. This last question resulted in the brief detention of General Bradley; although he gave the correct answer (Springfield), the GI who questioned him apparently believed the capital was Chicago. Although this behavior is often ridiculed in fictional depictions of the battle, it did succeed in identifying a number of infiltrators, many of whom didn't speak fluent English or know anything about American society. There's also a legend about a German spy who was caught because he could recite the entire "Star-Spangled Banner" when no true American knows anything past the first verse. Other things that gave the infiltrators away were that the Germans would pack four men in a jeep and drive it with the black-out slits on the headlights. The well-equipped US troops drove one or two men per jeep, and being used to their side having air superiority didn't bother with the black-out covers.
- Similar to the above, the parts of the French Resistance that helped Allied pilots back to England often quizzed the airmen they were helping. They often came across pilots who had knowledge of their unit, but none of their supposed home town, who were immediately detained as a possible mole. Once, they had a pilot who was the opposite — knew everything about his homeland, but nothing about his unit. Fortunately for him, one of the Resistance members was able to contact the RAF and established that he had been transferred there as a replacement from another unit, then immediately put on a bomber that was shot down over Europe.
One Allied pilot who was shot down and hidden in a barn by some locals found himself woken in the middle of the night by someone jabbing him in the gut and screaming at him in German. He reflexively protested in his native English, which served to prove to the French partisans that he was not a German spy. He reflected later on that it was fortunate that he did not reflexively reply in German, which he had studied in school.
- As The Other Wiki states, it helps if there is some handy phrase that your side can pronounce but which the enemy find difficult. One such example is Denmarks prized porridge rødgrød. It was so hard to say that rødgrød med fløde (literally rødgrød with cream) has been used by the Danish to catch infiltrators in BOTH World Wars.
- There have been accounts of World War II German soldiers spotting careless spies at rallies because they saluted wrong.
- Likewise, other careless slips, such as cutting and eating a steak the wrong way.
- One Hetalia: Axis Powers skit told a similar story about a German Spy in France: He was found out when he ordered a meal with a whole cooked potato. Apparently, Germans mash a whole potato while Frenchmen dice it.
- Or, in one case, a colorblind POW that wasn't aware that British and German uniforms were not the same color.
- According to US Air Force tradition, the Challenge Coin became a tradition during World War I after an American pilot who had been shot down, captured by the Germans, then later escaped, having only a medallion with his unit's insignia engraved on it (his identification documents having been confiscated by the Germans). This at a time when it was common for infiltrators to don enemy uniforms to sneak into enemy camps and conduct recon and sabotage.