Cyclops: Prove it.
Wolverine: You're a dick.
[beat, Cyclops drops his hand]
Undercover agents and victims of a "Freaky Friday" Flip will occasionally use Something Only They Would Say to positively identify themselves. Also handy in figuring out which twin is the Evil Twin, or when you're in the middle of a Twin Switch (though just as often, it's keyed off of Out-of-Character Alert).
Compare You Just Told Me, Ironic Echo, Cover Identity Anomaly, So Crazy, It Must Be True, and Bluff the Impostor. No One Else Is That Dumb is a Sub-Trope. If it's something that anybody from a particular group or with specific knowldge can answer, that's Only the Knowledgable May Pass. Contrast Out-of-Character Alert where a character wants to remain unidentified but say the identifying phrase out of habit, which at best makes someone just a touch suspicious.
- Afro Samurai: Possible Played for Laughs example. At one point during Afros fight with the Afro Droid, Ninja Ninja gets temporarily confused as to which is the real Afro.
Ninja Ninja: Youre bleedin, bruh. W-wait a minute, prove to me that youre you. Say somethin to let me know its you.
Afro: (has said this to Ninja Ninja on more than one occasion) Shut. Up.
Ninja Ninja: Oh, it is you!
- Ah! My Goddess: When Urd splits into good and evil parts, she actually does this to herself, saying "if you're the real Urd, you should know where Keiichi has his dirty magazines, etc." Followed by answering those questions.
- Cool Old Guy Joseph Joestar is forced to rely on this in JoJo's Bizarre Adventure Part 3. After being killed by Dio Brando and having his blood drained by the vampire, he undergoes an emergency blood transfusion to try to bring him back to life. Upon awakening and seeing Dio's corpse, his first thought is to play a joke on his grandson, Jotaro, and pretend to be possessed by the vengeful spirit of Dio. Jotaro is ready to punch his face in, but Joseph narrowly avoids being killed a second time by answering questions from Jotaro, such as "Who starred in the 1981 remake of Tarzan?" (Bo Derek) and "Who sang 'Eat It?'" ("Weird Al" Yankovic). As Jotaro puts it, "Only you would know such stupid things."
- Used as a red herring in Case Closed, where Jodie is routinely seen using a catch phrase ("A secret makes a woman a woman") belonging to Vermouth, the Black Organization's master of disguise, who bears some resemblance to Jodie. Turns out that Vermouth said the same phrase to Jodie after killing Jodie's parents.
- Played with much earlier in the series, in episode 2: Conan reveals he knows about the mole on Agasa's butt to try to convince Agasa he's really Shinichi in a kid's body - but Agasa just assumes Shinichi's been blabbing. Instead, Conan convinces Agasa by doing a Sherlock Scan to figure out where he's been, proving he's really Shinichi via ability instead of knowledge.
- Also when Akai Shuuichi is disguised as Okiya Subaru, he says "the blame is fifty-fifty", a common phrase he used, which provides the clue of who Akai was hiding as to Jodie after she realized his death was faked.
- In the end of the first season of K, the Silver King shows up in the body of a high school boy, and before he can worry about how to convince the others in the room that it's really him, the Gold King calls the phones in the room. When Kusanagi answers, the Gold King tells him, "There should be a man standing somewhere near you with a silly look on his face. Put him on the line, will you?" Sure enough, Kusanagi looks up and the Silver King is wearing that exact expression - after not having seen the Gold King for about seventy years, it still holds true.
- In the second episode of Valvrave the Liberator, Haruto has somehow found himself in the body of a Dorssian spy (who we will later come to know as L-elf). After rescuing his friends, Haruto tells them it's really him. How does Kyuma decide to test this? Several rounds of rock-paper-scissors. Haruto loses all of them. "Alright, it's you."
- In an early episode of YuYu Hakusho, Yusuke's deceased spirit possesses Kuwabara's body to tell Keiko that he's coming back to life soon, so he needs her to take care of his body. However, Yusuke's been unable to convince anyone else that he's been telling the truth, so instead, he approaches her from behind, suggestively compliments her "Nice skirt!" (a callback to a scene in the first episode where he flipped her skirt) and grabs her breasts. This causes her to slap him across the face while shouting "Yusuke, you jerk!" out of habit, after which she's much more receptive of his claim to be Yusuke in Kuwabara's body. Since that wouldn't fly outside of Adult Swim, the Bowdlerised Toonami version cuts out the boob-grabbing.
- In Baccano!, Rachel and her associates at the Daily Days figure out that the Rail Tracer was actually the train conductor, because the Rail Tracer knew Rachel was a stowaway and asked for her ticket.
- Later, Claire Stanfield reveals himself to Rachel as the aforementioned rail tracer by making a comment about her ticket purchases.
- You know how that demon that started the whole thing is always saying "maa, ii"/"well, no matter"? You know how that guy Ronnie who works for the Martillos is always saying the same thing?
- In Sailor Moon, Chibi-Usa knows that a monster disguised as her mother is a fake, because her mother calls her "Small Lady," not "Rabbit," which is the Black Moon clan's name for her. A similar situation occurs in the Sailor Moon: Another Story game, where Nergal disguised as Sailor Pluto is given away because she calls Chibi-Usa "Princess," while Sailor Pluto would normally use the same "Small Lady" nickname.
- Also in one of the final episodes of Sailor Moon S, Mistress Nine reverts to using Hotaru's regular body to get Moon to give her the Holy Grail (the "Purity Chalice" in the U.S. TV broadcast version). When Moon finds her among the ruins of the Mugen Academy, she realises the person she is talking to is not Hotaru when the latter calls her by her civilian name, Usagi: the real Hotaru met Moon before but only as Usagi, so Hotaru would never know that Usagi was Sailor Moon.
- In an earlier episode, as Usagi is being given a ride by Haruka, she recognizes the latter's speech about "people only surviving by trampling on others" as the same words Sailor Uranus spoke.
- Pretty Guardian Sailor Moon has a great, if narmy, scene, where Sailor Moon exhausts herself trying to protect Tuxedo Kamen and nearly falls down the stairs. Tuxedo Kamen catches her and asks if she's an idiot. SM automatically retorts with "who are you calling an idiot" before realizing their dialogue mirrors the one between her and Mamoru after the latter saved her from being run over by a car. Cue dramatic unmasking.note
- In both the Visual Novel and anime of Fate/stay night, Archer says and does things occasionally that hint at his true identity as a future Shirou Emiya, most damning of which is "Trace on", the same thing that Shirou always says when he activates his magic.
- In Fullmetal Alchemist, Edward and Ling are wary of one another since either one could be the impostor Envy, while trapped in Gluttony's stomach. Ling proves himself to Edward by offering to recite, in perfect order, all of the items on the room service menu from the hotel where they were staying. He then starts to press Ed's Berserk Button by making a reference to his shortness; when Ed pitches his characteristic tantrum, Ling knows he's the real thing. Ironically, when Envy does show up, they aren't even bothering with a disguise.
- Zigzagged when Bido recognizes the second Greed due to his signature speech. While he correctly identifies Greed as a result, Greed himself doesn't recognize Bido until after killing him and suffering when his lost memories come back.
- Later, after Greed's Anti-Heroic BSoD, Ed discovers Ling in the hut they used as a fallback after Mustang's guys, the Elrics, and Ling's party worked together to capture Gluttony (interestingly the last place in the normal world Ling was seen alive, really, since the two of them got to Father's base by way of Gluttony's stomach) and Ling's falling over and asking for food is taken by Ed as a sign that it's really him.
- Parodied in episode 14 of 4koma Theater:
Roy Mustang: "When we're alone, the Lieutenant calls me cutie pretty lovely lighter!" (gets shot twice)
- The above is a parody of an actual line used between Riza and Envy when they corner him. Roy has gone on the warpath against Envy when Envy revealed he killed Hughes. Riza inverts the trope by putting a gun on Roy and seemingly invoking this by saying that when alone, Roy always called her Riza. The Roy turns out to be Envy in disguise who ends up just confirming it is him due to Riza's trickery.
- A variant from when Ed asks both Alphonse and Winry what the latter told Al when they were kids for why she wouldn't date either of the brothers. Both of them answer that Winry told him she doesn't date guys shorter than her. Because this a memory of Al that Ed had no idea before he asked, it confirms that Al's soul really is bound to the armor.
- Akumetsu's mask in the eponymous series really isn't that good for concealing his identity, what with leaving much of his face including his distinctive hair and eyebrows and most of his grin visible, but it's by his 'ya know' that our initial viewpoint character recognizes him in the first arc. When he comes in and coincidentally kicks off his terrorist career by chopping up the Dirty Old Man who'd just hired her in her new career as a teen prostitute with an axe. They're both normal high school students again the next day. (Her for real, him only apparently.)
- He doesn't care all that much if he's recognized, since Akumetsu has a policy of dying on the job and any one of him probably has an alibi, and if he doesn't who's going to believe that the terrorists are a clone army, even after dissecting dozens of identical bodies? Also, the one who saved her wasn't the one she actually knew, even though they're all bizarrely similar for several dozen identical twins brought up separately, right up to the 'ya know.'
- The scene gets a callback later, though, with one of the not-important-enough-to-be-targetted minion with the underwear on his head tracking the girl down because she said 'Shou!' when Akumetsu came in and said his Catchphrase.
- In the final episode of Durarara!!, Mikado guesses that someone in a chatroom is Kida. The response? Grading Izaya on a scale of 1-10 with the square root of three, a callback to an earlier scene with the pair.
- Happens with Tetsuya in Metal Fight Beyblade. He wears a (actually very convincing) disguise to try and steal all of Ginga's beypoints, but is recognized at the last minute because of his alias 'Nigel Crabbypants'. Being openly obsessed with crabs does have a downside! Who knew?
- In Soul Eater, when Maka first shows up in the black room, Soul wonders if she's just an image created by the Little Demon. Her response is to hit him over the head with a book, something only she would do. After that, he admits that "Yeah, it's Maka."
- During the Chunin Exams arc, Sasuke gives Naruto and Sakura a lengthy passphrase to identify them with, since there are enemies about who might impersonate them, despite Naruto's complaints. Naruto goes off to relieve himself, and upon return identifies himself with the correct phrase. Sasuke promptly beats up the imposter, as the real Naruto wouldn't be able to remember it and complained about it beforehand. Predictably, when the real Naruto shows up to help out, he admits that he forgot the passphrase completely.
- Defied during the fourth Ninja World War arc. Chouji proposes something to this effect to make sure that they aren't being impersonated by white Zetsus, but Shikamaru says that the clones have been able to fool the ninjas with this method, as "Sometimes a lucky guess ends up being right". Only Naruto has a foolproof way of telling the real ones from the fakes and this is due to his recent powerup allowing him to sense different chakras.
- In Zone of the Enders: Dolores, i, James realizes that the Orbital Frame Dolores is connected with his supposedly-dead wife when he hears her singing a lullaby she used to sing to their children.
- This is how Leafa finds out Kirito is really Kazuto in Sword Art Online when he blurts out of his plan to save Asuna from Sugou's clutches as this reminds Leafa that he has feelings for Asuna.
- In Gintama, this is how the Yorozuya gang ends up identifying all of the players they run into while playing Monkey Hunter as people they know outside of the game. Some examples include Katsura using his Catchphrase, and Hasegawa lamenting the fact that he's unemployed.
- Katsura is especially prone to this in general, as referring to him by anything other than his name frequently prompts him to use his Mad Libs Catchphrase in the format of "It's not *noun*, it's Katsura!". He's managed to blow his cover on multiple occasions because of this.
- This trope plays quite a role in Honoo no Alpen Rose: One of the final proofs that Alicia/Jeudi's blind mother Helene needed to deduce that the one calling herself "Alicia" was not her daughter but a Body Double was whether she knew or not the "Alpen Rose" song, composed by Alicia/Jeudi's Disappeared Dad Friederich. The false Alicia, Mathilda, had claimed not to remember the song due to Trauma-Induced Amnesia. The real one, Jeudi, recalled the song enough to either write down the lyrics (manga) or sing it in public (anime).
- Aquarion Evol has a variant. When "transfer student" Jin can identify an attacking Abductor by name, Yunoha is able to make the obvious connection.
- A variation occurs in an episode of Pokémon — Serena meets a girl who introduces herself as Ariana (actually Kalos Queen Aria in disguise) and challenges her to a double battle, during which she makes a particular pose while giving orders. Later on, Serena watches one of Aria's performances and sees her make the same pose, at which point she puts two and two together.
- In Pokémon Adventures, X realizes that Y is actually Essentia in disguise when she 1) doesn't immediately apologize for separating from him and 2) calls him 'anata', which roughly translates to 'dear'.
- A non-verbal variant occurs in the opening battle of Mobile Suit Gundam Wing: Endless Waltz, when Duo is attacked by a unique enemy mobile suit, and after noticing that its method of fighting is to simply empty as many bullets in his general direction as possible, he recognizes that Trowa is the one piloting it.
- One of the hints before The Reveal that Largo was a resurrected Brian J. Mason in Bubblegum Crisis was boasting to Priss "This is the look of the true winner!", which were the words he said to Sylia at the start of the battle that originally killed him. The English dub added to this by having Largo call Leon "little puppy", which he also called Leon as Mason.
- Used in Overlord (2012) when the leader of a group of adventurers hastily claims they came to the Tomb of Nazerick on behest of an old friend of its ruler. Ainz has been looking for such old friends and holds his assault, asking who the message is for. The adventurer says it's for Ainz Ooul Gown...and promptly outs himself as a liar. The correct answer was either Momonga, Ainz's gamertag from when YGGDRASIL was an MMO, or Satoru Suzuki, his real human name.
- The Promised Neverland: Isabella is seen humming to an unspecified melody a few times. Near the end of the first arc, we learn that this was a song written by her Lost Lenore Leslie. When she discovers Ray humming it, she realizes that he's her son — he remembers her singing it to him while she was pregnant with him. Because he noticed her singing it too, he found out sometime before that that she was his mother.
- Solty is taught a song, "Return to Love", by Rose. When she sings it around Roy, he realizes that Rose is his missing daughter Rita, because that song only exists on a rare record that he used to play for his family to listen to.
- At the end of the anime, Roy and Yuto are able to find Solty in the debris of space when they hear her humming the song.
- A Certain Magical Index: Spoofed late in New Testament, when Shiage Hamazura is trapped inside a full-body suit he cannot remove, he tries this method to convince his girlfriend Takitsubo that's it's really him inside the suit. Unfortunately, the things he tries saying to convince her are not only embarrassing to her, but they are things he'd noticed since they started living together that she didn't know he'd noticed (mostly revolving around her morning and bedroom routines and hygiene). She and the rest of ITEM start attacking him thinking he's a pervert who'd put hidden cameras in her bedroom.
- Inverted in The Quintessential Quintuplets when Ichika tries to confess to Fuutarou by posing as Miku because she didn't have the courage to do it as herself (and also to sabotage Miku's own confession). Fuutarou quickly calls her bluff because, at this point, he knew the real Miku was in love with him and she would never say that.
- My Hero Academia: At the end of the first round of the Joint Training Arc, Jurota has Shinso on the ropes when he hears Hiryu's voice telling him to look behind him. At first, Jurota thinks it's just Shinso using his support item, right up until the voice refers to him as "Apocabeast", a nickname Hiryu came up with when they were alone. Sure enough, it's the actual Hiryu trying to warn Jurota before Tsuyu tongue-whips them into each other.
- In That Time I Got Reincarnated as a Slime, Rimuru and Benimaru come up with a pass phrase for Rimuru to check if he lost his rationality after becoming a true Demon Lord, with the test consisting of Benimaru asking about Shion's cooking and Rimuru answering that it stinks. Following his ascension to a Demon Lord, Benimaru asks him for the pass phrase... while Shion is holding onto Rimuru. Rimuru is able to Take a Third Option from his Ultimate Skill Raphael by saying that he is suppose to say Shion's cooking stink and that it was Benimaru's idea, thus diverting Shion's wrath (and cooking) for the time being.
- Daredevil: in the first appearance of DD's ex-girlfriend Elektra, he reveals his identity when he addresses her by his old nickname for her.
- Ms. Marvel: Beyond the Limit:
- Done unintentionally in the third issue. When Kamala is confronting the doppelgänger, she mentions that she "could murder ten gyros right now". Nakia remarks that that's definitely their Ms. Marvel, since it's a well-established character trait of hers that she's a Big Eater.
- In the fourth issue, Kamala convinces Nadia that she's the real Ms. Marvel by reminding her of a specific snack they shared when they were getting Nadia's citizenship paperwork sorted out.
- W.I.T.C.H.: In the original comics, Taranee gets captured and tortured by Elyon and convinced that anything she sees is an illusion. When Will comes to retrieve her, Elyon tries to convince Taranee that rescuing Will is an illusion created by her too. But Will says that she's telling the truth and Taranee can read Will's mind if she wants to verify, and Taranee figures it out because Elyon never knew Taranee could read minds.
- In Nightwing: Year One, Dick confronts Commissioner Gordon for the first time in his new guise as Nightwing. After Gordon prompts him to "say something only the kid would say" to prove his identity, Dick struggles for a bit before declaring "Holy Mistaken Identity!"
- In The Return of Superman, Lois Lane asks one claimant to the name Superman why she should give him the time of day. His answer? "To Kill a Mockingbird," which Lane recognizes as the real Superman's all-time favorite movie. Later on, to remove any shred of doubt in Lois's mind, he whispers to her, "No matter what happens, I will always love you. Always," which was one of the last things he said to her before he died.
- In the Donald Duck story "Kappa! Kappa! Kappa!", Donald's nephews see what looks like an ancient famous samurai show up to save kappa from the villainous tengu. They quickly realize the samurai is just Donald Duck in disguise...after they see him running away in panic in Donald's distinctive way.
- In one early The Flash story, this nearly gets Barry in trouble when, while in costume and conversing with a crime scene investigator, he gives the guy a wink that only Barry (as a police scientist) would give him whenever in agreement about something. Naturally, the other cop starts putting two and two together, but Barry manages to convince him by the end of the story that he and Flash are not the same person.
- During Stephanie Brown's run as Batgirl, at one point Clayface forms into an exact copy of her to try to escape a bank robbery. After the two Batgirls shout the standard "Shoot her!" "No, shoot HER!", one Batgirl turns to the detective and declares, "Shoot me. I'll bleed." Detective Gage promptly shoots the other one because no one else would come up with such a stupid plan.
- My Little Pony: Friendship is Magic:
- During the "Return of Queen Chrysalis" arc, the Mane 6 are affirmed of the CMCs' identity because of their talk of getting their cutie marks from being fillynapped (cue deadpan "It's them" from Applejack).
- In issue 65, a disguised Princess Celestia finally convinces Twilight Sparkle of her identity by saying she remembers the first time Twilight cast the "spell of Promethea", and Twilight knows Celestia promised to never tell anypony else about what happened.
- Peter Parker!Spider-Man does this twice in the finale of Superior Spider-Man. The first time, he attempts to convince Spider-Man 2099 that he's the real deal and Doc Ock had control of his body. Miguel realizes that it is so stupid it makes sense and buddies up with him. The second time, he goes to confront the Green Goblin, who still thinks it's Octavius controlling Spidey. When the Goblin boasts that once the bombs go off, he'll have nothing left, Peter retorts "Except the dignity of knowing I never carried a man-purse", Gobby realizes He's Back!.
- In a variant, a later issue has the Avengers see a report about Spider-Man fighting a villain who can manipulate and destroy clothes, so he ends up in only his mask and a web-diaper. While Captain America still isn't sure, Spider-Woman declares this must be Peter, because that kind of nonsense could only happen to him.
- The following issue has Peter going through numerous scans by the Avengers to make sure he is the real deal until they start talking about the time Octavius had bonded with the Venom symbiote, making sure from Captain America that the symbiote went back to his friend Flash Thompson... then decks Cap for hiding Flash's identity from him. This was Cap's proof Peter was back.
- And in Dead No More: The Clone Conspiracy, Spidey is pretty blasé about fighting a clone of Dr. Octopus. After all, that's not even the first clone of a dead villain he's faced that day. Even when Octavius calls him "Dr. Parker", he just figures the Jackal told him. Then Ock uses the phrase "the Superior Spider-Man", which only the actual dead Dr. Octopus (or a relatively recent Brain Uploading thereof) would know about.
- In Warlord of Mars, Dejah Thoris' grandfather Tardos Mors is presumed dead after a rebellion in Mars' North Pole and is discovered alive inside a ruin in their own kingdom thousands of miles away from where he died. Any doubts that he is an impostor are quickly dashed when he reminisces about a riding incident that only he and Dejah know about, confirming his identity. This turns out to be a subversion, as this "Tardos" is revealed to be a clone created by a telepathic entity that probed their memories and exploited this trope to gain their trust, while the real Tardos really is dead.
- In an issue of Kurt Busiek's The Avengers, the Avengers were thought to be a group of impostors. Carol Danvers was able to prove they were the real deal by reminding a guard of a casual threat she'd made to him years earlier, something an impostor couldn't possibly have known.
- In the Original Sin tie-in for The Avengers, the heroes encounter a time traveler who claims to be an adult version of Franklin Richards, the young son of their friends from the Fantastic Four. He proves his identity to Black Widow by mentioning an anecdote from his childhood where she showed him how to make Improvised Weapons out of his toys.
- A micro-issue of Teenage Mutant Ninja Turtles (IDW) follows Donatello through a day in his life—from his routine Flame War with an internet forum poster to his run-in with a petulant genius, Harold Lillja, at a convention. The turtle ninja realizes Harold is the aforementioned flamer when he uses the forumer's pet phrases, like "obstruse". Harold deduces who Donnie is as well, and promptly tries to kill his internet rival.
- One story in Doctor Strange involved Shuma-Gorath creating an illusion of Dormammu, who stated that he was there to reclaim his title as Strange's arch-nemesis from Shuma-Gorath. Strange saw through it right away because he knew that there was absolutely no way that Dormammu would ever admit to being second at anything, even with a being as out of his league as Shuma-Gorath.
- Issue 54 of Marvel Adventures Spider-Man has a Something Only They Would Have Heard variation; Spidey blows his secret identity to Captain Stacy when, after knocking two goons out before he could finish his quip, he remarks that "it's lonely being the smartest guy around", which Captain Stacy said moments before to Peter Parker.
- In Superman: Heroes, set shortly after Clark reveals his secret identity, he's worried Jimmy Olsen might break off their friendship now he knows he's been lying to him. It turns out that Jimmy already knew.
Jimmy: I used to think there were only two people in the world who called me "Jim." Then I realized it was only one.
- Frequently used in DC's war comics, based on the real-life practice of American soldiers asking each other baseball trivia questions to root out German spies. In Unknown Soldier #205 a G.I. remarks that he can't use the old "Who won the World Series" question because German intelligence knows that one by now — so he asks who Popeye's girlfriend is.
- Rocket (2017): A nearly perfect infiltration of Castor Gnawbarque III's office goes all screwy when a disguised Rocket orders a drink. He asks for a Gargle Blaster, not the preferred brand of the guy he's imitating, while his ex is in the room. She immediately draws a gun and shoots him.
- Immortal Hulk: Villainous version. The Hulk figures out who has gotten into Sasquatch with just two words: "Little. Monster." And then one of the most vicious versions of the Hulk has a Freak Out.
- Abraxas (Hrodvitnon): This happens a couple times with Monster X in regards to half of it being an Inhuman Human Vivienne Graham. It's Played Straight when Monarch become aware of this and Madison asks it a series of questions only Vivienne would know the correct answers to. Later, Susan is convinced of the truth about Monster X when she hears San and Vivienne's respective voices reciting the Elder Futhark and Frere Jacques, both of which are associated with Vivienne on a personal level in the story.
- And So We Fight has Impa immediately figuring out Sheik is Zelda through the song she played.
Impa: I know that song because I taught it to you, Zelda.
- Subverted in Hard Reset: In an early loop while engaged in a Beam-O-War with Celestia, Chrysalis (as Celestia) convinces Twilight she's the real one by telling her to attack them both, knowing Twilight would believe this is something only the real Celestia would say.
- Dæmorphing: When Toby and the Animorphs investigate the Ralek River, they ask each other questions to make sure the others aren't the ship's Andalites in morph.
- In Escape from L.A., Tom morphs into Jake, and tries to convince Marco that he really is Jake by sharing anecdotes of events that Marco doesn't know Tom was around to witness.
- After Doopliss swaps bodies with Mario in chapter 43 of Paper Mario X 2, the real Mario is left alone with the pig who has been following the team — who is revealed to be Kirby. Kirby is relunctant of joining Mario, asking for proof that he's the real deal. Mario then brings up the ending of the first Paper Mario X to Kirby (triggering a flashback in the process). Kirby then claims that only the real Mario would remember their goodbye.
- In Supernatural fanfic series "Sky Verse", Sam, Dean and Castiel realize they are vulnerable to impersonation and being tricked into an ambush by their enemies due to their use of cell phones to arrange to meet so they agree on passphrases they must use at the beginning of each phone call which are things they would never normally say and which their enemies would not be able to guess.
- In chapter 6 of The Sweetie Chronicles: Fragments, this allows Sweetie Belle to figure out that Elusive is Rarity.
- Subverted in chapter 47 of Variant Strain, where MJ tells Hank in Peter's body that telling her something only the two of them would know isn't enough because she knows about the memory-sharing thing.
- In Turnabout Reunion, the way Phoenix realized he was talking to Rainbow Dash was due to her calling him Nix, the same nickname she gave him when they first met.
- Eugenesis: Galvatron is trussed up in a room, and hears a person who sounds uncannily like Optimus Prime telling him to tell the Autobots what he knows, and then he will be let free. Galvatron eventually talks, and is released and told he can go. This is when he realises that is Optimus, because no other Autobot would ever let him go free. The problem is Optimus is supposed to be dead.
- Ripples, Waves, Tsunamis: When Nami's memories finally break through to the surface, this is how she confirms her identity to Raijax, and vice-versa.
- The God Empress of Ponykind; Celestia realizes just who she's fighting when Nightmare Moon calls her "Emperor". Tzeentch is the only being of Chaos who ever called her "Emperor" instead of "False Emperor", "Corpse God" or "Anathema".
- Played with in Background Pony. Every time Spike has "met" Lyra, he says, "Dig the swell hoodie." Until Chapter XVI, because it's really Discord in disguise. She doesn't realize it until it's too late.
- In chapter 65 of the Turnabout Storm novelization, Maya is channeling Trixie's grandfather, changing herself into a pony in the process. Trixie is completely unimpressed and calls the whole thing a fake, unless she gets proof that she is indeed talking to her grandfather. What Shadowmoon the Illustrious tells Trixie afterwards proves it, since only he and Trixie knew about it until then.
- Inverted in Memoirs when the only way Akagane can prove he's not a figment of the protagonist's imagination is to say something so ridiculously out-of-character that the protagonist realizes his imagination could never have come up with it.
- In Midnight Star: The Frozen Empire, Chrysalis's secret that all changelings are actually her children is something that she has kept hidden for millennia. When Midnight Star reveals this fact to her after explaining her own past, it convinces Chrysalis she's telling the truth as her counterpart would have been extremely desperate to even think of telling it to a pony.
- Bring Me Back Home has a subversion: when Ladybug goes ice skating with Chat Noir, he gives her the same instruction that Adrien gave Marinette a few hours earlier: "Just step, step and glide." She picks up on it and asks if it's a common thing to say. He says it is, so she doesn't think any more of it.
- This trope is noticeably common in Miraculous Ladybug identity-reveal fanfiction either in the straight form, where either of them choose to blow their cover to each other this way; or — more often — doing this by accident, saying something the other has heard their other identity saying. It's on the way to becoming a Fandom-Specific Plot on itself.
- In Lady Luck (Miraculous Ladybug), this ends up being the reason why there's no Mutual Masquerade between Lady Luck and Chat Noir like in the canon series. During her first outing with the Ladybug Miraculous, Chloe ends up tangled up Chat Noir and hears him joke about their situation. She guesses that he's Adrien from his puns and snarks at him for it, only to see that he's now Chat Noir. Likewise, Chloe's Lame Pun Reaction cues Adrien who she is, meaning both of them know the other's super-hero identity before the glamour could prevent recognition.
- In Time Fixers: Nicktoons of the Future, SpongeCog breaks into HQ after disguising himself as Timmy and his ruse is broken when he agrees with Jimmy that science is always the answer. When the adult Nicktoons are searching the place for him armed with weapons, Jimmy and Timmy, and Danny and SpongeBob run into each other and ask questions such as "What was the first insult Timmy called Jimmy when they met?" and "Who was the one who defeated the Syndicate's Doomsday Device?"
- In How the Light Gets In, Laurel is suddenly and inexplicably resurrected. While Dean, Oliver, and Sara all quickly decide it really is her, Felicity insists they test her somehow. She initially decides to do it by offering Laurel a glass of wine, only for Sara to flip out insisting with the trauma she's been through, that's unacceptably cruel. Dean eventually settles on this:
Dean: Laur, imagine it's the Superbowl. The Seahawks are playing. We're throwing our annual party.Laurel: We throw amazing Superbowl parties.Dean: Everything's going great. And then I tell you I'm rooting for the other team. What do you do next?Laurel: (disgusted) I immediately file for divorce. noteDean: That's my girl.Diggle: Well, sounds like her to me.
- In Heart of the Inferno, the third part of The Heart Trilogy, Smaug meets the aged Bilbo Baggins in Rivendell and sneaks in the hobbit's room in his human form. Though Smaug makes blatant references to their first meeting, Bilbo (who has never seen Smaug in his human form) doesn't recognize him until Smaug calls him "thief in the shadows".
- Innocence and Experience has Robin using a very distinctive slang word in front of Tim Drake, who's familiar with Dick Grayson and heard him dropping this very same word. Whoops.
- Rei regaining all her lost memories in Advice and Trust is marked off by her calling Kaworu a "stupid fish". Notably, many of the memories shown feature Kaworu referencing The Princess Bride.
- In the Beast Machines fic "The Dinobot Saga: Episode 1", Rattrap realises that the newly-reformatted transformer is Dinobot when he initially assumes that he's in a "Maximal torture chamber", which reminds Rattrap of the last time someone made that assumption.
- In A Colder War, the true nature of the entity possessing astronaut Shipley is confirmed when he describes the super-soldier serum as enhancing everything within the subject, a description that would only be known to Steves closest friends and HYDRA as most modern sources on the serum describe it in a more scientific manner.
- In Blank Slate, when Professor McGonagall learns that James and Lily Potter have been alive but amnesiac for the last fourteen years, Remus and Sirius accompany the next group to 'test' them; Sirius initially visits as Padfoot, with James confirming his identity when he yells at the dog to "Transform and use your damn words!" when Padfoot keeps barking at him.
- Hiccup in Persephone manages to get Stoicks attention by telling him that his mother/Stoick's wife is alive. At first Stoick thinks it is some underhanded trick, but he slowly starts to believe him when Hiccup draws him a portrait with too much detail for him to falsify. They strike up a deal; Hiccup escorts him to Valkas location, Hiccup can hold off on telling him where the Red Deaths nest is and Stoick spares Astrid and Toothless until then.
- Batman spends the first half of Batman: Melody for a Mockingbird drawing a blank for who is trying to destroy Bruce Wayne's life. Finally, the mystery man mentions Cloak and Dagger, a Calvin-ish board game Bruce made up as a kid. It brings Bruce to an instant realization this is his childhood friend and the game's co-creator, Tommy Elliot.
Absent's mother and Nathan (shocked): CORBIN?!
- oghond has never seen LF's face in pictures, or heard her voice. In the first chapter, when LF first appears, oghond does not recognize her due to this reason. That is, until LF speaks, using words that would be Sesquipedalian Loquaciousness for a German learning English. It's her sophisticated manner of speaking that allows oghond to realize who it is.
- Two chapters later, in "A Coder on Board," oghond's best friend Absent is turned into an Oshawott. Upon waking up and realizing he is now a Pokemon, oghond at first doesn't recognize him, but does think he sounds somewhat familiar. She just can't place the voice until Absent turns to HP - who just saved his life - and remarks "Pride yourself." As oghond puts it:
And all at once the identity of the person clicked with those two words.
My eyes widened in recognition.
There was only one person I knew who said "pride yourself" in that way. Which is odd, considering that the phrase itself is pretty common, but here's the rub: no-one else I knew who had said that phrase said just that phrase.
No one else except...
"Absent?" I gasped.
- Two chapters after that, in "Hostile California," it's Absent who does this- twice, both times to members of his family and both times in order to prove his identity after having been turned into a Pokemon. The first time he does it, it happens as soon as he enters the house. His mother and brother, Nathan, do not recognize him at first- until Absent notices the family dog. Almost immediately, he calls out "Come here, stupid!", causing the dog to stop glomping his brother and start glomping him. The reason it counts as this trope? Only a member of the West family (and oghond, but that doesn't matter here) knows that the dog answers to both her real name and "stupid." With Nathan already in the house, there's only one possible conclusion as to who the Oshawott at the door could be...
- Later on, he does it again to his father, who- despite having heard his voice on speakerphone- is still slightly disbelieving as to the fact that his son is an Oshawott. This is until Absent apologizes for failing to "bequeath unto [his father] that boot to the head." It's a Mythology Gag— the real Absent once showed his father a video called "Last Will and Temperament," in which... well, see for yourself.
- In Sword Art Online Abridged, Healthcliff gets exposed as Kayaba because of his fascination with pop culture references nobody else gets (and how he makes a Call-Back to something Kayaba said back in episode 1).
Heathcliff: Oh, so now you've seen TRON!
- A meta-example in Persona 5: Hoshi to Bokura to, when Akira first wakes up in the Velvet Room, the line Igor greets him with confirms to the readers, that in this version of events, Yaldabaoth did not seal away Igor and impersonate him.
- In The Power of the Equinox, the canon example from the second season finale of My Little Pony: Friendship Is Magic is made mutual. Dimmed Star (the recently transformed Twilight Sparkle) is on the verge of killing Princess Cadance in hateful fury, unaware that the Cadance who imprisoned her in the underground caves is an impostor. Wanting to die with happy memories in her mind, Cadance starts reciting the song she and Twilight used to sing. Dimmed Star stops in her tracks and continues the song, after which both mares finish it in unison. This leads to Cadance realizing that the monstrous mare who almost ate her is actually Twilight, and Dimmed Star learns that she's been dealing with an impostor of her former foalsitter.
- A Diplomatic Visit: In chapter 5 of the second sequel, Diplomacy Through Schooling, when Pharynx sees where Thorax has led them for his bachelor party, he thinks this may be an impostor... until Thorax whispers something to him that convinces Pharynx of his identity.
- An unusual variation in Canary's Wrath. Oliver sees Laurel kill Damien Darhk, talks with her, learns she's the Spectre, and kisses her. Shortly after she leaves, he's informed she also killed Malcolm Merlyn. It takes hearing that, for him to conclude yes, that was definitely her.
- Played for Laughs in Shadow Realm: Fifteen. Tessa is faced with two versions of Fifteen, one of which is the shapechanging Copycat, and has a gun with one bullet. She first asks them to say something only they would know, only for both to give an acceptable answer. She then asks for the name of her boss, only for both to give the correct answer at the same time. Finally, she asks them what her number is. One yells, "How the hell should I know?" while the other says it. She shoots at the one who didn't give an answer, only for him to use the other Fifteen as a Human Shield. The human shield turns back into Copycat and dies, and the real Fifteen points out that Tessa has never actually told him her number.
- In A Pairing Of Souls, Shen Qingqiu convinces people he reverted to his pre-qi deviation persona when he starts spouting insults and sneering at Luo Binghe and Liu Qingge (respectively "beast" and "brute").
- In Queen's Checkmate, Futaba demands proof that the being talking to her is a part of her (specifically her Shadow). Shadow Futaba responds with an Among Us meme, which is enough to convince Futaba.
- Ma'at: To confirm Dani's identity after a Super Gender-Bender:
She should be able to convince Dominic or Gunther of her identity. They'd been on enough digs that one or another of the near-blackmail stories they had on each other should overcome their disbelief.
- The Reaping of Hatsune Miku (Vocaloid & The World Ends with You): After coming Back from the Dead, Luka goes to meet with her friends and needs to convince Meiko that it's really her. Her high-school sake stash and chocolate orders aren't sufficient, so she tries something... a little more personal.
Meiko: (muffling her) Oh my god you're Luka.
Len: Collection of silver what?
- Jasmine is tipped off to Prince Ali's identity when he asks her, "Do You Trust Me?". He also rolls an apple down his arm and throws it to her with his elbow, a trick he does as both Aladdin and Prince Ali. The animator who drew Jasmine's facial expression when she realizes this deserves an award.
- The old man whom Aladdin meets in the dungeon says "prin-cess" like Jafar does. He's revealed to the audience to be Jafar immediately after, so most people don't even notice.
- Anastasia: During Anya's interview with Sophie, Sophie specifically asks how she escaped the siege on the Winter Palace. Vlad and especially Dmitri think the jig is up since they never prepared her for that question, only for Anya to remember a servant boy who "opened a wall". Dmitri immediately recognizes this because he was that servant boy, and realizes she's the real princess because she's one of only three people who would've known that. This happens again when Anya does finally get a chance to talk to Marie. Marie initially brushes her off as an actress, albeit "the best one yet". It's not until Anya recalls an intimate memory about spilling Marie's peppermint oil on the carpet and lying on that spot whenever Marie left the country that gets her to reconsider. Bringing out the matching necklace and music box and singing their lullaby seals the deal.
- In Barbie as the Island Princess, the only thing Ro can remember before she got amnesia is the song, "Right Here in My Arms". At the end of the movie, the Queen and Ro realize that they're mother-daughter because the Queen used to sing it to her daughter.
- Batman Beyond: Return of the Joker:
- The Joker introducing his return in Neo Gotham in front of an elderly Bruce Wayne. Bruce is in stunned disbelief, but his old arch-nemesis assures Bruce that it really is him because "after all, who'd know me better than you". This also foreshadows the flashback revealing that the Joker had managed to discover Bruce Wayne was Batman shortly before he was killed... the first time.
- Batman, gunning for the Joker near the end, runs into the ex-Robin Tim Drake instead. Before Batman can take him to a hospital, Tim addresses him by his secret identity, Terry McGinnis. Batman asks how Tim even knew that, before Tim calls him by another name: "Batfake", the Joker's pet handle for the current Batman. Tim then proceeds to transform into the Joker.
- Syndrome in The Incredibles tells Mr. Incredible "I am your biggest fan...", which makes Mr. Incredible realize Syndrome is actually the grown-up Buddy Pine.
- In Megamind, everyone calls the setting Metro City except for the title character, who pronounces it to rhyme with atrocity. When he's fighting Titan disguised as the superhero Metro Man in the climax, he accidentally gives himself away when he mentions the city's name. The only reason Titan knows this is because he heard Megamind say it dozens of times as a news cameraman.
- A non-verbal version happens in The Lion King (1994). When Simba fights a lioness that was trying to eat Timon and Pumbaa. Simba is eventually defeated by the lioness when she uses Nala's trademark flip-and-pin move on him, the same one that Nala used to beat him when they were cubs. This causes Simba to realize the lioness he is fighting is actually his best friend Nala.
- Similar to the example above, in Reign of the Supermen, when Lois confronts the returned Superman following his Dynamic Entry, she asks what was the last secret he told her before he died. It was "I love you".
- In The Secret of NIMH 2: Timmy to the Rescue, when they were kids, Martin, jealous that Timmy was the prophesied hero of Thorn Valley and not him, derogatorily called his brother "Hero". Years later, when Timmy reunites with Martin, who had become hyper-intelligent and took over NIMH, he recognizes him through his changed appearance when he says...
Martin: I suppose I have changed a bit. But for the better, don't you think, hero?
- In The Transformers: The Movie, after Megatron's death, people are suddenly surprised by the arrival of a new, purple-and-black robot who crashes Starscream's coronation. Then he opens his mouth and smugly demeans the Decepticon's new leader before easily killing him.
Starscream: Who disrupts my coronation?!
Galvatron: Coronation, Starscream? This is bad comedy.
Starscream: ...Megatron? Is that you?!
Galvatron: Here's a hint! [transforms into a laser cannon and reduces Starscream to ash]
- In An American Christmas Carol the ghost of Jack Latham convinces Slade he's the real deal by telling him information only he'd know.
- The protagonist in The Assignment (1997), a Carlos the Jackal lookalike undercover as the real deal, proves his identity to his handler when his handler says "awfully warm for this time of year", to which he replies "but not as sticky as two summers ago". These are the two halves of a code phrase that was part of an assignment from long ago that his handler mentioned in conversation.
- The Batman films use this trope often:
- In Batman Begins, after being asked who he was under the mask, Batman subtly reveals his secret identity to Rachel Dawes by mirroring a statement that she made to Bruce Wayne earlier in the film, when she caught him in public playing up his Rich Idiot With No Day Job persona and he tried telling her that that wasn't the real him.
Bruce/Batman: It's not who I am underneath, but what I do that defines me.
- In Batman Returns, Bruce Wayne and Selina Kyle accidentally expose their identities as Batman and Catwoman to each other by unthinkingly reenacting a snippet of banter from their previous fight. In a slight variation, they switched lines in and out of costume.
Batman/Selina: Mistletoe can be deadly if you eat it.
Catwoman/Bruce: But a kiss can be even deadlier... if you mean it.
- And this trope is also used in Batman (1989) and is how Bruce realizes the Joker is the thug who killed his parents. He repeats the phrase to Joker at the beginning of their final confrontation just before decking him.
Jack Napier/Joker: You ever dance with the devil in the pale moonlight?
- A villainous example happens in Batman & Robin. While Poison Ivy is seducing Robin she claims she can see him having his own "Robin Signal" in the sky. Later, she steals the Bat Signal and replaces it with Robin's symbol, and Robin, remembering the conversation, instantly realizes it is Ivy calling him, believing the signal to be a sign of her love to him.
- In Batman Begins, after being asked who he was under the mask, Batman subtly reveals his secret identity to Rachel Dawes by mirroring a statement that she made to Bruce Wayne earlier in the film, when she caught him in public playing up his Rich Idiot With No Day Job persona and he tried telling her that that wasn't the real him.
- The Blues Brothers: Matt "Guitar" Murphy knows that the only two white guys who will walk into a soul food restaurant "dressed like Hasidic diamond merchants" and order dry white toast, four whole fried chickens and a Coke are Joliet Jake and Elwood Blues.
- Cinderella (1965) has Prince Christopher seem to recognize Cinderella, whether she's wearing rags or a ballgown, when she returns his thank-you's with, "You are most kindly welcome."
- A version of this occurs in Disney's Condorman, although it's not so much about identity as intent. Natalia and Woody (the titular hero) are sharing a moment together when he says the line, "I'll bring the dip if you bring the Dostoyevsky." Later, when it appears that she has changed her mind about defecting, she says it back to him, which prompts him to realize that she wants to be rescued after all.
- In The Count Of Monte Cristo, Fernand Montego is confronted by the Count immediately after finding the king chess piece he gave sixteen years ago to Edmont Dantes, his former best friend whom he betrayed and sent to a hellish prison. He doesn't make the connection until the Count/Edmond reminds him of their old game.
Fernand: Monte Cristo.
Edmond: King's to you, Fernand.
Fernand: (drops the chess piece in shock) Edmond?
- In The Crow, Sarah only realizes that the corpse-painted stranger who saved her from being hit by a car is her deceased friend Eric when he quotes the Arc Words "It can't rain all the time."
- In Elf, Buddy attempts this with a fake Santa. It... doesn't work.
Buddy: If you're Santa, then... what song did I sing for you on your birthday?Fake Santa: Uh, Happy Birthday, of course!Buddy: Darn!
- The movie Face/Off uses a physical gesture of affection in this way. Specifically John Travolta's "smell my hand" gesture.
- From Ghost: the word "ditto", which Patrick Swayze's character would use to respond to "I love you", to the point where his widow refuses to believe it's him when he tells her those three words through a medium.
- Zartan from G.I. Joe: The Rise of Cobra is quite fond of whistling the tune to "Jolly Good Fellow". When the man we think is the President comes out of the bunker, he goes into his office, relaxes and begins whistling. No prizes for guessing the tune.
- In the film adaptation of Harry Potter and the Goblet of Fire, Barty Crouch Jr., who is disguised as Mad-Eye Moody, nearly blows his cover when he performs a familiar facial tic (specifically licking his lips) in front of his father. Technically he does blow his cover, it's just that the father doesn't live long enough to spread the news.
- The Hunger Games: Catching Fire: How Finnick Odair convinces Katniss he's on her side — he tells her "Remember who the real enemy is."
- In Indiana Jones and the Kingdom of the Crystal Skull, a character (Mack) tries one of these (he tells Indy a betrayal is "just like Berlin", where they were double-agents), which fails. The guy was really a traitor anyway.
- In The Italian Job (2003), the villain realizes that he's on a date with the daughter of a man he killed years ago when she uses her father's trademark phrase, "I trust everyone; I just don't trust the devil inside them."
- Jack Frost (1998): After dying in a car accident and being resurrected as a snowman, Jack eventually manages to convince Charlie that it's really him as a snowman by calling him "Charlie boy" (which is what Jack used to call him by). Gabby, however, doesn't believe Charlie when she tells her the snowman is her husband. That is until Jack calls her on the phone, nonchalantly asking her to come to the cabin in the mountains, and Gabby recognizes her husband's voice and obliges.
- In the James Bond movie The World Is Not Enough, oil heiress Elektra King and terrorist Renard give themselves away as conspirators by using an identical aphorism - 'There's no point in living if you can't feel alive'. A few minutes later, Renard jams his hand into Bond's injured shoulder—something else he could only have learned from Elektra, though when Bond confronts her about this, she points out that Bond has been wearing a sling and any number of Renard's spies could have told him about this.
- Possibly invoked in the trailer for The Jungle Book (2016), which is narrated by Scarlett Johansson. The viewer might not realize who she's playing at first because she's simply narrating generically and ominously...but even if you didn't see who was talking, you'd know who it was the minute she said her last line, and it makes The Reveal of her character's identity all the more shocking.
Kaa: Trussssst... in me...
- Just Like Heaven: David visits Elizabeth's sister to try and persuade her not to turn off Elizabeth's life support. On the way there he asks Elizabeth's spirit, who only he can see, for "dirt" on Abby to convince her that he's really speaking to her sister. Elizabeth supplies a few childhood anecdotes but David stresses it needs to be something only a sister would know. Elizabeth provides the story of Abby kissing her ex-boyfriend on her wedding day. David uses the story when he speaks to Abby but all it does is freak her out and she chases him out of her house.
- L.A. Confidential: when he's become the victim of a Have You Told Anyone Else?, Jack Vincennes says "Rolio Tomassi" as his dying words. That was the name Edmund Exley had just entrusted him with in a private conversation, and is a name he made up for his father's unknown killer, 'the guy who gets away with it'. When Dudley Smith gets nervous about who this "Rolio Tomassi" might be and what he might know, he starts asking around about him... to Exley, who realizes immediately that Dudley should have no way of knowing that name and confusing it with a real person unless he had something to do with Jack's murder.
- Played with in The League of Extraordinary Gentlemen, after the Big Bad and The Mole have just attempted to destroy the Nautilus with planted explosives. The Mole, who has stowed away on the escape vessel with the bad guys, manages to send a message to the rest of the League with the coordinates of the escape route. They immediately realize it's from him because of the way the message opens - he's the only one in the world who would address them collectively as "my freaky darlings."
- Marvel Cinematic Universe
- Avengers: Age of Ultron: Ulysses Klaue realizes Ultron is one of Tony Stark's creations when Ultron, after transferring a ten figure sum of money to Klaue for his vibranium supply, says, "It's like I always say, 'Keep your friends rich, and your enemies rich, and wait to see which is which.'" something Tony used to say.
- Captain Marvel (2019): Carol explains early on this is the easiest way to test if someone is being impersonated by a Skrull, as they only retain a stolen identity's most recent memories. Fury figures out Talos has impersonated his boss when he calls him "Nicholas", since he'd told Carol that nobody, not even his mother, calls him anything other than "Fury". This gets a call-back when a Kree soldier appears to be taking Fury, Maria and Skrull prisoners to be ejected out an airlock. Leaning in to Fury, the Kree says "Just go with it... like Havana." Fury realizes this is actually Talos using Fury's own Bluff the Imposter move from earlier to reveal himself.
- Spider-Man: Far From Home: After getting a violent and heartbreaking heads-up as to exactly how detailed Mysterio's illusions can be, Peter calls in Happy Hogan for a ride and asks for "something only [he] would know" to confirm he's talking to who he wants to see. A confused Happy recalls when he chaperoned Peter in Germany for the Avengers' civil war and they stayed in a hotel together; Peter ordered a pay-per-view movie for which Happy got the bill, and although the name wasn't listed, Happy could tell from the price that it was an adult film, and Peter didn't know how he would know that. Peter, now convinced it's actually Happy, cuts him off before he can say anything more embarrassing.
- In Doctor Strange in the Multiverse of Madness, the titular character tells a variant of himself about the death of his sister Donna as a child to convince him that hes the real thing as its something he never talks about to others.
- The Matrix Revolutions:
- Bane (whose mind has been overwritten by Smith) reveals himself to Neo by addressing him as "Mr. Anderson" in his usual mocking tone three times. Neo is slow to catch on, if only because of how inconceivable it is to believe Smith is walking around in the real world using another man's body.
- Happens again in the final battle when Smith says, "Everything that has a beginning has an end, Neo" — revealing that the Oracle is still in there somewhere.
- The climax of Muppets Most Wanted involves Miss Piggy almost marrying Constantine, a master criminal impersonating Kermit. When the real Kermit crashes the wedding, Miss Piggy comes up with a way to distinguish them: she asks each in turn to marry her. Constantine confidently says 'Yes, I will! Let's go right now!', while the real Kermit stutters awkwardly and tries to duck the issue.
- The phrase "As you wish" in The Princess Bride is the Former Trope Namer. Westley, Buttercup's love, has been presumed killed, but turns up as the Dread Pirate Roberts, and Buttercup recognizes him by his use of the phrase which, for him, meant "I love you." For bonus points, he gives her vague hints at first, and when she tells him "You can die too for all I care!" as she pushes him off a cliff, he shouts it as he rolls to his (apparent) doom. (This leads to a My God, What Have I Done? moment for Buttercup. She and Westley both get better.)
- Nickelodeon's original movie Rags, a Cinderella-esque story, has the protagonist (a Cinderfella) meet with the music star (equivalent of princess) at a masquerade ball, and on his way out he tells her, "Be you." Later, when she seeks his help to track down the mystery singer Rags, right before the auditions start he repeats his earlier line, inadvertently revealing himself and later saving himself from having his Secret Identity and big break stolen by his evil stepfather and stepbrother.
- On Chesil Beach: The film jumps to 1975, where Edward is working at a record shop. A young girl asks him for a Chuck Berry record, and when she explains her reason for wanting it, Edward realizes the girl is the daughter of his old love Florence. The girl tells him that her mom thinks Chuck's music is "merry and bouncy," something Florence used to tell him.
- In Ransom, Tom Mullen knows for sure Jimmie Shaker is the mastermind when he hears him say "Shouldn't be a problem": a phrase he heard over and over when an FBI analyst was examining a recording of an earlier conversation between Tom and the kidnapper.
- Happens twice in the original RoboCop (1987), one of which is non-verbal. Lewis initially recognizes Robo as Murphy when he spins his pistol by its trigger guard in the precinct firing range, a trick Murphy had copied from his son's favorite TV show. Later, Robo confronts one of Boddicker's gang members and repeats the same line with which he tried to arrest the goon the first time around, which freaks him out to no end.
Robocop: Dead or alive, you're coming with me.Emil: (disbelieving) Wait a minute, I know you... you're dead. We killed you. We killed you! WE KILLED YOU!!
- The Secret (2007): Ben is convinced that Hannah is really in Sam's body due to her relating anecdotes from their past and speaking the way that she did. At first he just thinks Sam must have heard it from Hannah, but soon accepts that it's really her.
- In The Sixth Sense, this is how Cole demonstrates his medium powers to his mother, by repeating several things that only his grandmother's ghost would know.
- In Spies Lies And Naked Thighs, a man is introduced as a secret agent who has been surgically altered to resemble an old friend of the main characters in order to stop an assassination attempt on two world leaders. Late in the film, one character who knows that the assassin is hiding nearby manages to tip him off with a signal from college which meant "There's a girl in the room", revealing that this agent is really the old friend.
- In The Ten Commandments (1956), Moses calls Master Builder Baka "Master Butcher" after he's willing to see an old woman killed rather than momentarily pause a construction project. Later on, while disguised as a Hebrew slave, Moses sees Baka whipping Joshua and attacks him, putting him in a choke-hold while calling him "Master Butcher." Baka has a brief Oh, Crap! moment of realization before he's strangled to death.
- In Terminator Genisys, at one point Kyle and Sarah are separated from Pops (the friendly Terminator) and wonder if he's not being impersonated by the shapeshifting T-3000 when they reunite. However, Pops' wordy and technical explanation for why he can't shapeshift immediately convinces Kyle that he's the real one.
- Amusingly invoked by Malone in The Untouchables (1987) despite the other person being a complete stranger:
Eliot Ness: Wait a minute! What kind of police have you got in this goddamn city, huh? You just turned your back on an armed man!
Malone: You're a Treasury Officer.
Eliot Ness: Yeah, how do you know that? I just told you I was!
Malone: Who would claim to be that who was not?
- Wild Things. Cops are doubtful of a young woman's claim that her guidance counselor raped her, due to her promiscuous, troublemaking reputation. But they believe her when not only does another victim come forward, she reports the identical Post-Rape Taunt that the first victim did—"no little bitch can ever make me come".
- In Wonder Woman (2017), Diana realizes that British politician Sir Patrick Morgan is actually Ares_the God of war and the film's Big Bad_when he reveals himself by saying, "You were right, Diana. They don't deserve our help. They only deserve destruction", something only Ares would say.
- In the first X-Men movie, Wolverine has just dispatched the shapeshifting Mystique and is confronted by a suspicious Cyclops. When challenged to prove that he is himself, he calls Cyclops a dick. Given that the pair had squabbled all throughout the film, Cyclops accepts this as proof.
- 2666: Lotte realizes that Archimboldi is really her brother Hans, based upon the descriptions she read in one of his novels.
- In A Brother's Price, Jerin's sister Blush was outside, and when she returns, cannot remember the password. This causes her to use some colourful curses, so that they already know it can only be her when she finally remembers the password. (They all learned how to curse from their grandmothers. Other families in the area probably don't have quite the same vocabulary...)
- In Eldest, the 2nd book of the Inheritance Cycle, Eragon recognizes the dragon rider in steel armor as his seemingly dead friend Murtagh when he spins his hand-and-a-half sword at his hip, much like he did when the two of them trained together.
- "Jane Smith" was identified by her bizarre taunt ("Rub a monkey's tummy! Rub a monkey's tummy with your head!") in the children's book Wayside School Gets a Little Stranger.
- In Harry Potter and the Deathly Hallows, the good guys use Polyjuice potion to create six decoy Harrys while traveling. However, Harry sees the face of someone he knows in the crowd attacking him. He attempts to disarm him, rather than stun or kill, and the Death Eaters realize that this one is him; Harry, being a Technical Pacifist, also used Expelliarmus in his battles with them. (In the film, it's Hedwig coming to the rescue which gives him away.)
- In the same book, Voldemort jinxes his own name so that whoever says it is immediately found. The only people brave enough to do that, rather than referring to him by euphemisms or "the Dark Lord", are the ones leading the fight against him.
- Then there's the passwords the Ministry suggested everyone set to identify impersonators. Mrs. Weasley's password to her husband was her husband's pet name for her — the embarrassing/adorable "Mollywobbles".
- In the light novel The Disappearance of Haruhi Suzumiya (volume 4), Kyon uses an alias known only to him and Haruhi to get bizarro-Haruhi to listen to and believe his words, and makes a mental note to keep it as an emergency measure from then on.
- Mask (2020): Side-Splitter makes an announcement over the radio about sinking every battleship on the sea. His finishes off his broadcast by saying "We'll stop at nothing, even when it's raining gnats and frogs.". This causes Akiko to freeze up in horror, because that's the phrase her mom likes to use instead of "it's raining cats and dogs". This confirms in her mind the suspicions that her mom is working with The Doll Lady and Side-Splitter. Thankfully, her mom actually works for Room 12.
- This was used time after time in Sweet Valley High, because of all the Twin Switches that were going on. In one example, the twins' friends prove which twin is which by asking Jessica to spell thief and asking Elizabeth who a certain soap star is. Jess spells it wrong and Elizabeth doesn't have a clue about the soap star. Somehow, their friends are convinced...
- In another book, Enid (Elizabeth's best friend) and Todd (her boyfriend) are convinced that Elizabeth has told another guy everything about them when the guy repeats to them things they told her. When he tries the same thing with Jessica, she calls his bluff and later realizes that he stole Elizabeth's diary.
- In Stone of Tears, the phrase "true as toasted toads" is used to positively identify a messenger as having come from Zedd.
- Also subverted in the first book. Richard finds himself under the effects of an "Enemy Web", where people would perceive him as their enemy; Darken Rahl if they're Richard's ally, or as Richard if they were allied with Rahl. Richard sneaks into his brother's tent, gets his attention, and goes to do the "Loser's Salute," which his brother forced him to do whenever he lost one of their play swordfights as kids, to identify himself. But his brother already recognizes him as Richard; this immediately tips Richard off that his brother was really in league with Rahl.
- A bit later, Zedd recognises Richard despite the Enemy web because she notices his habit of running a hand through his hair when frustrated.
- In the last book, after using forbidden magic to save the world from some other forbidden magic (yeah, that happens a lot in this series), Richard believes that his wife's feelings prevented her from regaining her memories, which she lost as a result of the latter forbidden magic. He realizes she did regain her memories when she says, "You're a rare person, Richard," something she said about him during the first book.
- In The Lord of the Rings, Aragorn quotes to Frodo a bit of poetry that Bilbo wrote about him. Frodo knew the poem not from Bilbo, but because it was in a letter from Gandalf that he (Frodo) was reading right then. Aragorn did not know that the poem was in the letter, although he might have known or suspected that Gandalf would supply Frodo with that line, making it a reasonable thing to drop into the conversation.
- In the third book, Sam gives Frodo the password "Elbereth" to lower a ladder in the Tower of Cirith Ungol, reasoning that "No orc would say that".
- In Body Parts by Michael Bates, the tip off is the way a girl says "difícil" just as the protagonist's friend used to before she went missing. What's it a tip off to? The fact that the girl was sewn together from body parts harvested from local kidnapped teens, including said friend, which (somehow) gives her an unconscious retention of their mannerisms. This is a bit different from usual, as the girl herself doesn't know the identities of her "donors".
- In The Stars My Destination by Alfred Bester, Saul Dagenham recognizes a disguised Gully Foyle when he uses a pseudonym that Dagenham had implanted in Foyle's mind back when he first attempted to interrogate him via hypnosis.
- In Kushiel's Mercy, even though Sidonie's under the influence of Fake Memories wiping out the memory of her boyfriend Imriel, and Imriel himself is a Manchurian Agent, the use of the word "always" when it comes up in conversation always triggers something for them, which they eventually figure out. ("Always" is NOT the trigger to unlock Imriel's true personality, but it seems to help the two blend together.)
- In Unicorn Point, Bane accidentally reveals himself when he speaks a Phaze dialect in place of Mach's Proton-speak.
- In Xanth there is a Sorceress who likes to possess people. Unfortunately, she often gives herself away by calling people "my pet". Also, the Demoness Metria is described as being easily recognizable, no matter what form she takes, because of her speech impediment (luckily, her alternate personalities have no such speech problems).
- Played for laughs in the Culture novel Matter. When an Upper-Class Twit-turned-fugitive seeks help from his former tutor, the latter tests his identity through several questions, all of which he gets wrong. The tutor wearily concludes this is indeed his inept student of old.
- Star Trek: New Frontier, "Treason": Si Cwan (a ghost) proves he's possessed his sister by fighting both Xyon and Calhoun (neither slouches in the fight department), beating Xyon and getting beat by Calhoun, but proving himself enough for Calhoun to call him "Cwan, you pompous ass!"
- A variation in The Paths of the Dead: Tazendra (now a Lavode) is standing guard at Dzur Mountain when Piro and Kytraan arrive to see Sethra Lavode. Being Tazendra, she's ready to just jump down and attack them, but when she hears Piro use the exclamation "Cha!" she recognizes it not as Piro's Catchphrase, but as his father's, and she's happy to escort her old friend's son in.
- In the Dale Brown novel Flight of the Old Dog, Brad Elliot recognises a colonel at the Alaskan base the Old Dog crew are trying to get a tanker from and uses a few choice insults to identify himself.
- In Mark Billingham's novel Lifeless, the man responsible for a string murders is rumbled by DI Thorne when, during a phone call, he repeats a phrase he used in an incriminating videotape which Thorne had seen earlier.
- In the Gaunt's Ghosts novel Blood Pact, Tona identifies that she's from Gaunt with a message to Vaynom Blenner by reminding the latter that he lied about his father to Gaunt on the first day of scholam.
- In The Elenium trilogy by David Eddings, Sparhawk and other members of the Pandion order of knights have a long-standing code to identify themselves to one another. When traveling in disguise, Sparhawk sends a messenger to the home of a brother Pandion with the message that he "has brought his little mother for a visit." Little mother is the Pandions' term of endearment for Sephrenia, their tutor in magic. (She happens to be present for the dispatch, and is surprised to learn of the code in her honor.)
- Little Pet Shop of Horrors from the Bone Chillers series is about an evil pet shop that turns children into animals and sells them as pets. The protagonist has a friend who can do somersaults. At the end of the book she gets a pet dog. When it stands up and does a somersault, she realizes who it is.
- The Dresden Files:
- In the novel Ghost Story, Molly asks Harry (who's dead at the time) to prove he's not some supernatural nasty in disguise.
- In general, this is used many times over the course of the series as the heroes must deal with enemies who can shapeshift into another person's form. Harry even pulled this on Mab because she was speaking through an intermediary, something she had not done previously. So, she invokes his debt (her control over him) and makes him feel incredible pain.
- In the Liavek story, "A Well-Made Plan", a "Freaky Friday" Flip-ed character shows up at his front door and tries to convince his butler that it's really him. The butler asks what the item that is the source of his magical power is, and the character explodes in fury, refusing to reveal it, particularly since he'd never told the butler in the first place. This is the response that the butler was looking for, and he gladly lets him in.
- In the Discworld book The Truth, William recognizes the Big Bad as his father by a phrase he commonly used, "A lie can run around the world before the truth has got its boots on."
- Neatly inverted/played with in Ender's Game. Ender, depressed and unwilling to keep playing the titular game, receives a letter from his sister Valentine, which is full of various jokes and references that only they share. He realizes that she wrote it at the behest of his "handlers" in order to cheer him up, because it's too full of these references.
- Animorphs: After Sixth Ranger Traitor David acquires Marco's DNA, the others ask the real Marco Bluff the Impostor-type questions. He proves himself by giving characteristically smart-ass answers.
- A slightly modified version, "something only she would type", is used in Paper Towns by John Green. Quentin recognizes that a comment on the fictional Omnictionary website was written by the missing Margo, who has a habit of randomly capitalizing letters inSide worDs anD sentEnceS.
- An interesting variant in Emily the Strange: Stranger and Stranger. To determine which Emily is the right one, a game of Emily Jeopardy was created to determine who was the real Emily. The two Emilys came up with questions for the other.
- In Moon Rising, Moonwatcher's telepathic mentor note asks her to read a particular history book. It details Fathom's execution of Darkstalker, which was achieved through an enchanted artifact.
Moon: I wonder what he enchanted.
Her mentor: It was a bracelet.
- In the Star Wars Legends novel Vision of the Future, Han Solo arranged to meet Lando secretly. Knowing that Imperial forces may be monitoring his communications, he instructed Lando to meet him "Ten systems Coreward from the place where you had no choice." In other words, ten systems Coreward from Bespin, where Lando "had no choice" but to betray Han and his allies.
- In the Mistborn books there is a race of intelligent beings called Kandra who can use a persons (or animals) bones in order to perfectly imitate that person's appearance. They gain none of their memories, but will typically observe or interrogate the person before taking over in order to more effectively imitate them. Determining who has been killed and replaced with a Kandra is a major plot point in several books in the series.
- In Mistborn: The Original Trilogy Vin discovers a Kandra has infiltrated the group and spends a good deal of the second book trying to find them with the help of an allied Kandra named OreSeur. She asks various members of the crew about specific details of private events in hopes discovering the spy, but in the end Vin fails to find the spy ahead of time because the enemy Kandra, TenSoon, had actually replaced OreSeur, not one of the other humans.
- In the second Mistborn era book Shadows of Self a rogue Kandra is causing havoc throughout the city and attempts to assassinate the Governor. The main characters all set up unique call and response pass-phrases with each other in order to prevent the Kandra from replacing one of them, however the Kandra had already replaced the Governor at some point before the book started, making the phrases useless.
- In the "Whoops, I shouldn't have said that" form, this trope is used in Robert Goldsborough's Nero Wolfe novel Murder In E-Minor. Two people both use the same slightly-odd phrase to describe the state of their relationship, which tips Wolfe off that they've rehearsed their stories together.
- In A College of Magics, Tyrian is apparently killed in the final confrontation, but due to the high levels of magic rampaging about is still alive but occupying the body of one of the bad guys. This trope is how he persuades Faris it's him in there.
- While any human can speak the Master-Word and prove they're human, only the narrator/hero of The Night Land knows that Naani is the reincarnation of Mirdath, and only he knows that name or the story of their love in that previous life so many millions of years ago. He describes what he remembers of it to her to prove that he is the reincarnation of her lost love. (And that she's not crazy for remembering it.)
- In the backstory of The Witchlands, Ragnar decided to check if a monk famous for being able to track down anything was his missing son, a Scarily Competent Tracker. To do that, he sent out a letter asking to help find a missing dog called Boots (the name of the boy's beloved childhood pet), figuring that someone unfamiliar with the name would refuse such trivial request. It worked.
- In A Wind in the Door, Meg is tasked with figuring out which of 3 identical men is the real Mr. Jenkins. She asks them all how they plan to help Charles Wallace at school and realizes the real Mr. Jenkins is the one who is annoyed by the test and doesn't get what's going on, instead of spouting platitudes about what the school will do.
- In an episode of 3rd Rock from the Sun, Dick gets locked in the stairway of a dentist's office because he is so desperate to smoke a cigarette. When Harry finally finds him, he shouts through the door:
Harry: Wait, how do I know it's really you..?
Dick: It's really me!
Harry: Well, that's something you would know!
- Agents of S.H.I.E.L.D.:
- In the Season 1 finale, the message to Mike Peterson from his son to let him know he's been rescued includes something only they would say to prove it isn't a trick.
- In Season 5, Deke, a man from the future, recalls a phrase his mother would always say to him, which she claimed her mother would always say to her. Towards the end of the episode he hears Simmons say it, and realizes that she is — or rather, will be — his grandmother.
- Arrested Development:
- When Oscar has to convince Michael that he's not his twin brother George Senior:
Michael: No, no, don't buy it. I'm taking my son to the cabin, and there's nothing you can say to make me believe that you are not my father.
Oscar: I understand. Your child comes first.
Michael: Oh, my God, you're Oscar.
- When Buster is pretending to be George Senior and refers to Lucille as "mother":
Buster: I mean lover. I love making love to mother. I mean lover.
- And the mysterious pimp "Frank":
Michael: She's a...?
"Frank": Lady of the evening. Working girl. She turns illusions for money.
Narrator: And that's when Michael recognized the voice.
(Michael fumbles for the lightswitch)
"Frank": Don't you do it! Ain't nobody gonna see what Frank look like!
(Michael turns on the lightswitch, revealing none other than Gob, and his ventriloquist dummy Franklin)
- When Oscar has to convince Michael that he's not his twin brother George Senior:
- A meta-example in Babylon 5: G'Kar has a vision of an angelic being (in the form of his late father) telling him that it's up to him and his fellow Narns to break the cycle of violence between themselves and the Centauri, or both sides will be destroyed. G'Kar asks "Who are you? Where have you been all this time?" The response comes: "I have always been here" — and that's when the audience realises the angelic being is actually Kosh.
- Interesting variation in the final episode of Blackadder II. Blackadder has apparently sold out Queen Elizabeth to a master of disguise for a single key bit of information — in this case, Nursie's habit of dressing up as a cow at dress-up parties.
Blackadder: From this moment he was doomed. For you see, the prince is a master of disguise, while Nursie is an insane old woman with an udder fixation.
- Buffy the Vampire Slayer:
- In the episode "Dead Man's Party", Cordelia asks, "How do we know it's really you and not zombie Giles?", to which Giles responds, "Cordelia, do stop being tiresome," and Cordelia quips, "It's him."
- In the fourth season, Faith attacks Buffy in her home and activates a magical device during the ensuing fight. Afterwards Joyce asks her daughter if she's all right, and "Buffy" answers with Faith's Catchphrase ("I'm five by five"), letting the viewer know that a body switch has taken place. Later on in the episode, Buffy (in Faith's body) makes reference to the aforementioned episode of Giles-turned-Demon to prove to Giles it's really her. But not before playing with the idea:
Buffy: Giles, it's me, and I can prove it. Ask me something only Buffy would know.
Giles: ...who's President?
Buffy: We're checking for Buffy, Giles, not a concussion.
- Similarly, in the fourth season of Angel, Angel realises that Cordelia is possessed by the same power that is controlling the Beast when both use the endearment "my sweet".
- Cold Case:
- An episode has the detectives trying to deduce who planted a bomb that killed a married couple by interviewing the friends who had visited them the weekend before. It soon became obvious that the supposedly dead wife was in fact alive and pretending to be one of the friends in question (they bore a strong resemblance to each other)—it was the friend who died in the blast along with the husband—when one of the other friends mentioned hearing the wife say something very similar to what the woman had told them.
- In another episode, they deduce who the killer is when they realize that the inscription on the victim's tombstone is a Bible verse that one of the suspects quoted to them.
- In the Community episode "Conspiracy Theories and Interior Design" Jeff recognises that only the Dean could possibly have written Garrity's ridiculous lines.
- Criminal Minds: In "Revelations", the unsub has Reid hostage and is streaming the video to his fellow members of the BAU. When the unsub demands that Reid pick another member of the team to kill, Reid chooses Hotch, calling him a "classic narcissist", then quotes a Bible passage. The rest of the team thinks that Hotch takes this personally, but in fact he's analyzing everything Reid says for clues to his location; Hotch is well aware of his own flaws, and also knows that narcissism isn't one of them. He then looks up the Bible passage Reid quoted and discovers that Reid quoted it incorrectly, something which Reid, who has an eidetic memory, would never do. The correct Bible verse turns out to be the key to where Reid is being held hostage. Reid even tells Hotch after his rescue that "I knew you'd understand."
Hotch: Alright, everybody, right now — what's my worst quality? ...I'm all these [flaws], but none of you said that I ever put myself above the team because I don't, ever. Reid and I argued about the definition of classic narcissism and he knew that I would remember that, and he also quoted Genesis, chapter 23, verse 4 — read it. ...He wouldn't get it wrong unless it was on purpose.Morgan: He's in a cemetery.
- Doctor Who:
- "The Enemy of the World": The Second Doctor intends to prove to his companions that he's not the Identical Stranger villain Salamander by playing his recorder ... only he left it in the TARDIS, so he mimes playing it.
- In "The Christmas Invasion" and the "Children in Need" mini-scene that leads up to it, the Tenth Doctor demonstrates himself to be the same man as his previous incarnation by repeating to Rose the first thing he said when he met her in his previous body.
- "Midnight" has a strange "detect the enemy" variant on this: An alien being seems to possess a woman, and it keeps repeating whatever anyone says to it. The Doctor surmises this is its attempt at learning. Then it says things at exactly the same time as everyone else. Then it only does for it the Doctor. Then it speaks before the Doctor does... Eventually, the woman seems back to normal, and the Doctor seems to be possessed. The woman convinces everyone else to throw him out the airlock... but two characters realize the being has just stolen the Doctor's voice and is still possessing the woman when she uses two phrases the Doctor used earlier ("Molto Bene" and "Allons-y").
- "Turn Left" has the reappearance of "Bad Wolf" (series one's Arc Words) as a message from Rose to the Doctor, letting him know that holes must be opening between their parallel universes, which is very very bad.
- River Song has her personal way of calling the Doctor for help: graffitiing a significant historical artifact with her current space-time coordinates, along with "Hello Sweetie".
- "The Impossible Astronaut": The Doctor becomes suspicious of his companions behavior when they refuse to tell him about his future death at Lake Silencio. In order to prove he can trust her, the Doctor demands that Amy swear by something that matters.
Amy: Fish fingers and custard.
The Doctor: My life in your hands, Amelia Pond.
- When the Doctor hears the phrase "Run, you clever boy, and remember", he knows he's found Oswin/Clara again. Twice.
- "Nightmare in Silver": Clara Oswald asks this of the Doctor while he's fighting a Battle in the Center of the Mind. The Doctor starts admitting he's always been attracted to her, only to get an Armor-Piercing Slap which puts the Doctor's real personality back in control. As Clara points out, even if he did feel that way, he'd never admit it to her. Later, she asks the Doctor if he thinks she's pretty, and he insults her, satisfying Clara that it's the Doctor in control.
- Inverted in "The Night of the Doctor". As the 8th Doctor attempts to drag a woman to safety in the TARDIS, his assurance to her that it is Bigger on the Inside instigates a full-tilt freakout when she realizes that he is a Time Lord.
- "Dark Water" plays it for drama. After Danny Pink is killed, the Doctor and Clara travel to what may be the afterlife to get him back. However when Clara is put in verbal contact with Danny the Doctor is suspicious, and urges Clara to ask Danny something only he would know. Danny however is afraid that Clara, if convinced, will kill herself to be with him (unaware she's there physically) and manipulates her into closing the channel between them, something only the real Danny would do.
- "Thin Ice": The Doctor isn't sure if a particular nobleman in 1814 London is actually an alien in disguise. The mystery is quickly solved, however, when said nobleman is shocked to see Bill (who is black) in his house and demands "that thing" leave. Both the Doctor and Bill immediately agree that an alien wouldn't care about skin colour; that level of knee-jerk racism is exclusively human.
- "It Takes You Away": While trying to find out if the Grace in the Alternate Universe is real, Graham asks her to tell him about the frog necklace he's wearing. She remembers it perfectly, making him that much more reluctant to believe she's a fake.
- On Dr. Quinn, Medicine Woman, a visiting naturalist rapidly befriended the title character and her beau Sully. To that end, they all attended Horace and Myra's wedding, at which point Horace revealed that Dr. Mike and Sully have just gotten engaged themselves. Stunned, the man proceeded to offer the happy couple a toast, which includes the recitation of a beautiful poem, leaving Mike just as stunned, as the poem was precisely the one her presumed-dead fiancé recited at their engagement party. When she confronted him, after some badgering, he finally admits that he is in fact, the man in question.
- The episode "Jack of all Trades" has Jack swapping bodies with the Astreus's crew, starting with Fargo. At first Alison thinks Jack has gone crazy, and when "Fargo" corroborates, that he's playing along as some sort of joke. Then Jack tells Alison they were just making out, leading to this:
Fargo (in Carter's body): Dr. Blake, PDA in the workplace is against GD policy...
Carter (in Fargo's body): Bigger! Issues! Fargo!
Alison: Oh my God, you're not kidding.
- When Jack shows up just after a Jack impostor tries to kill Zane, Jack's attempt to explain how he got there tips off Zane to the fact that he's telling the truth.
Zane: No computer simulation of you could be that incoherent.
- The episode "Jack of all Trades" has Jack swapping bodies with the Astreus's crew, starting with Fargo. At first Alison thinks Jack has gone crazy, and when "Fargo" corroborates, that he's playing along as some sort of joke. Then Jack tells Alison they were just making out, leading to this:
- Variant: Watson asks someone who claims to be looking for Sherlock, "Are you a friend of his?" "He doesn't have any friends" is the right answer.
- An earlier episode also has an inversion. Holmes figures out who the killer-of-the-week is, but ends up being kidnapped. Earlier, Watson is shown to be frustrated about Holmes texting like a "teenager on a sugar high" with tons of unrecognizable abbreviations and emoticons (Holmes believes it allows for efficiency in communication). When the kidnapper tries to tell Watson that everything is fine, she uses Holmes's phone but texts in a normal manner. Watson immediately goes to Captain Gregson. After he's freed, Holmes tries to get credit for "deliberately" getting the kidnapper to text Watson.
- A character missing this was used in one episode of Family Matters, an episode that saw Steve Urkel bust a criminal and receive a death threat from his brother. This results in Carl and a fellow cop taking shifts in protecting Steve. For years, Carl had always said, "See you later," to that particular partner, who would always reply, "Not if I see you first." Later in the episode, when Carl left his watch, the "buddy" turned out to be the killer in disguise, but as he's about to kill Steve, Carl busts in with the police force and arrests him. As it turns out, the killer replied to Carl with a simple, "Yeah, see ya," letting Carl instantly know it wasn't him.
- Farscape: In "A Human Reaction", John Crichton crashes back to Earth and is immediately detained by the military who refuse to believe he's the real Crichton and not an alien impostor. Crichton's father eventually gets in to see him and asks John to tell him what they did for his tenth birthday. When John is able to finish the story they finally believe he's who he says he is. It eventually turns out that the whole trip back to Earth was a simulation and "Jack Crichton" is an alien who only knew the story about John's childhood from scanning his memories.
- A recurring bit of Father Dowling Mysteries was Frank having to deal with his twin brother, Blaine, a con artist who often posed as his priest brother for scams. The two are arrested together while dressed alike as Sister Steve is asked to figure out who's who. She asks Frank what a patron told him in confession and Frank says he can't repeat it. Steve knows it's him as Frank would never break the sanctity of confession, even to save himself.
- In the F Troop episode, "Wilton, the Kid" an outlaw called Kid Vicious, who is a dead ringer for Capt. Parmenter comes to town. In the climax, Kid dresses up Parmenter and ties him up claiming he caught the imposter. The others quickly realize off that the one tied up is the real Parmenter when he he trips and falls.
- When Maris goes missing for several days, Marty has police check her bank details. They find several of her cards have been spent in New York boutiques, but it's not until they confirm none of the purchases have been spent on food that Niles realizes Maris is safe. Then Frasier points out Maris is safe and hasn't bothered contacting him for several days while she went on a shopping spree.
- A later episode has someone delivering mystery gifts to Niles. He's uncertain it's Maris, who he's in divorce proceedings with, until an incident at Café Nervossa. A barista confirms that an elegant, well-dressed woman came in, and ordered an expensive latte... then took one sniff of it and left. Niles starts having a sobbing breakdown as he realizes that, yep, it's Maris.
- Game of Thrones: When Tyrion sends an offer of alliance to Jon on behalf of Daenerys, he closes with the statement "All dwarves are bastards in their fathers' eyes", a sentiment he shared with Jon back when they first met, in order to prove it's him.
- In an episode of Get Smart, Max is kidnapped by KAOS, who sends a highly-trained impersonator to take his place in Control. When the real Max storms into the Chief's office, the Chief sets up a panel to ask both "Smarts" several questions to decide which is the real one. For example, 99 asks both "Did you ever kiss me?" The fake Max says, "Don't you remember?" But the real Max says, "I'm not the kind of man to kiss and tell." Later it's revealed that the real Chief has been replaced by an imposter, too.
- In the Goosebumps TV adaptation of Stay Out of the Basement, Margaret knows which Mr. Brewer is her real father when the real one calls her by her Affectionate Nickname, "Princess".
- In the pilot of Graceland, Mike is on his first serious undercover operation and is ordered by Russian mobsters to kill Donny, a DEA undercover agent who had his cover blown. They end up in a Mexican Standoff and Mike is trying to convince Donny of what is going on but Donny never met Mike and is highly suspicious of Mike's story. Mike tells him that he just moved into Donny's old room in "Graceland", the house the undercover agents share, and that Lauren, Donny's fellow DEA agent, told him not to touch any of Donny's stuff. Since this is exactly what Lauren would have told the New Meat, Donny believes Mike and they lower their guns.
- In one episode of Hannah Montana, Miley's cousin disguises herself as Hannah to reveal her secret to the world. Lilly and Oliver stop her, but they can't tell the two apart. Oliver asks the girls if they want to kiss him. The fake one, who likes Oliver, agrees, while the real one says no.
- Subverted on Haven. A shapeshifter decides to do a Kill and Replace at Audrey's birthday party, and at one point, Audrey is suspected of being the imposter. She rattles off a bunch of personal information, like her favorite music and her middle name, in order to convince her friends she's not. Except she's so new in town that no one knows if any of that information is true. In the end, this Audrey is the imposter.
- In Living Color! parodies this in its fake trailer for Ghost 2. When Sammy Davis Jr.'s ghost tells the medium to relay to his wife he loves her, the wife says "Sammy would never say it like that". When faux-Whoopi tells her "Sh-Boing-Boing-Boooooiiiing", his wife instantly knows his spirit is there.
- In an episode of Jessie, Jessie and Zuri accidentally switch bodies with Ravi's magic bell. When Jessie goes to Ravi for help, Ravi doesn't believe her to be Jessie in Zuri's body until "Zuri" mentions that Ravi still wears choo-choo underwear which is a secret between him and Jessie.
- In the Law & Order universe, to ascertain if someone is an undercover cop, the other cops ask what the color of the day is.
Woman: "That's enough."Jack: "Sound familiar, does it?
- During the prosecution of a young woman accused of killing her mother so that she could have her stepfather all to herself, the DA's began to suspect that the girl was telling the truth—that the man had seduced her and killed his wife when she found out and threatened to both divorce him and have him charged with statutory rape. To that end, they called both the girl and the stepfather's new girlfriend into a conference room and gently asked the girl to describe what the man had said and done when making advances to her. The girlfriend's horrified reaction to what the girl was saying cinched it.
- In a Season 21 episode, a supposed heiress is found out when she uses "jughandle" to describe an offramp, exposing her really being from New Jersey.
- In an early episode of SVU, the detectives realize that a fellow cop is the Serial Killer who's been preying on prostitutes when they interview a survivor and note the way she shielded her eyes when the assailant blinded her with a flashlight (he was holding in the way cops are trained to do).
- In the Lifetime Movie of the Week "Video Voyeur" (Based on a True Story), a woman becomes uneasy as to how her neighbor knows things he couldn't possibly know. In particular, one morning, she declares that she's "having a bad hair day". When she encounters him later, he tells her, "Your hair looks fine!" She searches the attic above her bedroom and bathroom and finds cameras that he's set up to record her and her family.
- In Lois & Clark an identical brush of the hand on her cheek finally (and accidentally) clues Lois Lane in on the fact that her boyfriend isn't just a mild-mannered reporter.
- In Lost, The Man in Black is inhabiting John Locke's body; when he meets Richard, he says, "Hello, Richard. It's good to see you out of those chains," recalling a conversation the two had centuries earlier when Richard was chained to the walls of the Black Rock.
- In the second season, where Desmond is identified by his use of "brother".
- Happened in the previous season with the whole Red Sox thing that Sawyer hears Jack say (Sawyer heard it before from Jack's father, that even mentioned that felt bad and wanted to call his son).
- Marvel Cinematic Universe:
- Iron Fist (2017):
- When Danny Rand approaches Jeri Hogarth, she tests his claim that he's Danny by quizzing him about her workspace from when she interned at Rand Enterprises:
Danny Rand: Look you remember me, right?
Jeri Hogarth: No.
Danny Rand: Come on! You were an intern in the legal department at my dad's office?
Jeri Hogarth: Where was my office?
Danny Rand: Um...you didn't have one. They put you in the copy room.
Jeri Hogarth: My desk?
Danny Rand: Uh, it was a folding table, with a file under one leg because the flooring—it was too uneven.
- Danny tries this out with the Meachums, but fails because he only gives them basic information that could be looked up online (in Joy's case) or are too stubborn to believe him (in Ward's). He later breaks through to Joy via a shared habit from their childhood regarding brown M&M's, the only color they refused to eat.
- When Danny Rand approaches Jeri Hogarth, she tests his claim that he's Danny by quizzing him about her workspace from when she interned at Rand Enterprises:
- Jessica Jones (2015) has an inversion of this as Jessica and Trish plan their move to get up close to Kilgrave so that Jessica can kill him. They decide on a code phrase that Jessica will say so that Trish will know that Jessica still is not under Kilgrave's control. They realize that they cannot use something she would normally say because Kilgrave could just make her act like herself (as he just did with Luke), so they decide it would have to be something she would never say. Jessica decides to use the phrase "I love you", which turns out to be particularly handy at the episode's climax.
- Iron Fist (2017):
- In an episode of Murdoch Mysteries a female witness uses the word "huckleberry" to describe anyone she does not consider to be an upstanding citizen. When Murchoch later reviews the transcript of an old trial he discovers that the key witness in that trial also used the word "huckleberry" to describe people she did not like. He quickly discovers that the two witnesses were actually the same woman who was paid by an unscrupulous prosecutor to assume fake identities and act as a prosecution witness so the prosecutor could win more cases.
- Subverted on The Middleman, when Wendy asks MM this and he refuses to divulge secrets through a civilian interpreter. That's good enough to prove it for Wendy.
- NCIS: Los Angeles:
- A common bit is for the team (or other government agencies they meet) to have specific code phrases for security.
- A hacker is using intricate software to not only perfectly mimic the team's voices but even "deepfake" video likenesses. Nell calls up Kensi and Deeks, asking them to prove their identities by answering "what's Hetty's favorite tea?" As it happens, neither of them has the right answer but their bickering argument about it is enough to prove to Nell it's really them.
- By the next season, the team has run into so many "deepfakes" that they create special code phrases that sound like casual conversation. So when Callen answers a call from Sam with "Sam Hanna, greatest partner in the world" and Sam doesn't answer back with "I love you too," Callen knows this isn't really Sam. He calls the real Sam who answers with "G, my main G-man" with Callen giving the proper response phrase.
- In Now and Again, Michael Wiseman, killed but brought back to life by the government in a new body, makes use of this to insinuate to people from his past life who he really is.
- This was also used on NYPD Blue. The "color of the day" refers to a color that undercover officers wear to distinguish themselves from real criminals. If a bunch of cops raid a drug den, they might think twice before getting too rough with someone who's wearing, say, a green shirt if that's the color of the day. If you look at the blackboard behind Sipowicz's desk there's an entry for the color of the day, filled in each morning by Fancy (or whoever). Since NYPD Blue always strove for realism this is probably Truth in Television.
- The Once Upon a Time episode "The Thing You Love Most" has a variation: When Regina attempts to interrogate Mr. Gold about Emma coming to town, he asks her to "please" excuse him. This is the first hint to Regina and the viewers that he remembers his life as Rumpelstiltskin, since it recalls a conversation that they had in the Enchanted Forest: Part of his price to help her cast the curse is she must do whatever he asks when he adds "please" to the sentence. Regina only agreed to that condition because she thought she'd be able to rewrite Gold's memories with the curse.
- When Haley has locked herself in the tutoring center during a school shooting on One Tree Hill, she identifies her husband when he completes their catchphrase through the door ("Always..." "...and forever.") and lets him in.
- On The Orville Mercer and Kelly come to a spaceship with a video talk with Mercer's parents who make snide remarks on Kelly (who cheated on Mercer) and ask their son how his colon is doing. When they go onto the "ship", Mercer and Kelly are transported to an alien zoo. It turns out Ed's "parents" were just a hologram created to trick them into boarding the ship. Mercer has to give props to whoever programmed the hologram as that's exactly the way his parents would have acted.
- The Outer Limits (1963) episode "The Architects of Fear" features a poignant example. A man volunteers for a mission to be turned into an alien-like creature, climb inside a fake UFO and launch an "attack" against the earth. (All this as part of a plan by a shadowy organization to bring about world peace by uniting humanity against an external threat.) The plan goes awry however, when the "UFO" crashes and the grotesque "alien" is shot by hunters. The man's pregnant wife (who knows nothing about the mission) arrives on the crash scene and doesn't recognize the ship's alien-looking occupant as her husband—until he does a special pointing gesture that has special meaning for the two of them, just before he dies of his wounds.
- In Red Dwarf, Rimmer tries to discourage Lister from going ahead with his plan to become Rimmer's superior officer by posing as Kristine Kochanski (who Lister had a crush on and wants to revive as a hologram). Rimmer succeeds in convincing Lister that there's no point in doing it as "she" has no interest in him at all... until "she" says, "I want a man who's going places. Up, up, up the ziggurat, lickety-split!"
- In "The Inquisitor", after Lister and Kryten are erased from the timeline to make way his "sperm-brother" and another mechanoid, Lister convinces their counterparts of their identities by listing several embarrassing personal details about Rimmer, that only Lister could possibly know.
- Inverted in "Psirens", a shape-shifting, brain-sucking alien monster gets on the ship and looks just like Lister. The crew try various tasks that only Lister should know but the Psiren can read Lister's mind and so mimics every action perfectly. They finally trick it by giving one Lister a guitar and telling him to play. Lister is normally the Dreadful Musician so when this Lister plays the guitar like the ghost of Jimi Hendrix they immediately blast it (Lister only believes he can play that well).
- Sabrina the Teenage Witch gets impersonated by her Evil Twin, so her aunts have her say "woo-hoo" to see if she's the real one. Salem doesn't believe her, but Sabrina proves her identity by threatening to tell Zelda about the time he was in her lingerie drawer
- In the The Sarah Jane Adventures episode "The Man Who Never Was", Luke twice sends a message to Rani and Clyde by unconventional means. Both times he proves it's him by calling them "Clani".
- Conan O'Brien's Saturday Night Live sketch about Moleculo (THE MOLECULAR MAAAN!) has a superhero keep blowing his Secret Identity this way.
- Invoked Trope in Shadow and Bone. When Mal turns up at the Little Palace demanding to see Alina, Kirigan pretends to be skeptical, saying many people are claiming to be friends of the Sun-Summoner just to get a look at her. However surely a childhood friend would know what her favorite flowers were? Mal immediately replies, "Blue irises". It's no surprise we then see Kirigan presenting Alina with a posy of blue irises.
- Sonny with a Chance: When Chad starts using a Doppelgänger stunt double to impersonate him on every "dangerous" date with Sonny, Sonny manages to tell the two apart by messing up both their hair. The real Chad hates having hair messed up and quickly fixes his hair, while the fake one doesn't care at all.
- Stargate SG-1
- In "Crystal Skull", Daniel Jackson is shifted into another dimension that makes him invisible to everyone but his grandfather, who unfortunately is known to be slightly insane. Daniel instructs his grandfather to repeat some things after him to convince his team that he is standing right there with them. When a skeptical Jack responds in the usual way, Daniel frustratedly mutters "Jack, don't be an ass", which grandpa repeats word for word. Jack is taken aback and after a second he replies, "Daniel?"
- The situation is reversed in "Fragile Balance", where an infuriated "Daniel!" from a considerably younger version of Jack is taken as confirmation of his identity by Daniel (the two characters usually adopt a particular tone when speaking to each other). The actor who played Young Jack should have gotten an award for the brilliant job he did of mimicking O'Neill's mannerisms and speech patterns.
- The trope is lightly mocked in the episode "Spirits", where they encounter shapeshifting aliens:
Daniel: Jack. Are you you?
O'Neill: Yes. Are you?
O'Neill: Never mind.
- And again:
Daniel: Don't shoot! Just let them tend to Xe'ls.
Jack: How do I know you're the real Daniel?
Jack: ... Yeah, okay. [lowers gun]
- The second season episode "Holiday" also has a large dose of this. For example, when Jack and Teal'c have switched bodies:
Hammond: How did it go, colonel?
Teal'c (in O'Neill's body): It did not go well, General Hammond.
O'Neill (in Teal'c's body): Ya think?
- "Urgo" has a similar case as "Crystal Skull" above: Everyone in SG-1 has brain implants inserted in them on an alien planet which end up manifesting the titular Urgo, a person only they can see and hear. At the end of the episode they return to the planet and explain the situation to Togar who did this in the first place to get the implants removed. However, there is a problem: The implants will cease to function outside of a host brain, effectively killing Urgo, whose existence was an unintended side effect in the first place. The situation is solved when they convince Togar to take one of the implants himself. But with the implants removed, SG-1 can no longer see or hear Urgo, so how do they know he really survived?
Daniel: Wait, Togar, how do we know that Urgo's really alive?
Urgo: I'm here, I'm here, tell them, tell them!
Togar: I will as soon as you are quiet!
Daniel & Jack: He's alive.
- The ancient communication stones used in Stargate Universe seem to be setting up for a whole swath of this trope. The stones allow faster than light communication through the simple expedient of swapping bodies with the host receiver at the other end. It kicked off in episode 9 with one of the crew being allowed to visit her girlfriend/lover back on Earth, but doing so in the guise of a different body. Asked if it was really her, the [blue eyed, Anglo] stranger replied in fluent Cantonese "Have you thrown away that ugly red chair yet?", which satisfied her lover as to her identity.
- Star Trek: The Original Series
- In "Turnabout Intruder", Kirk, while trapped in his ex-lover's body, tried to convince Spock that he was him. He mentioned certain events where Spock had helped him and urged him to help him again. Subverted when Spock calmly pointed out that those events could be easily read from the captain's logs and reports.
- It's rather bizarrely subverted in "Whom Gods Destroy", where an insane former Starfleet officer develops the ability to morph into other people, and Spock is presented with two Kirks at the climax. He somehow can't come up with any questions that only Kirk would know, just so the episode can end with a fight scene. Leonard Nimoy himself was quite upset about it.
- In one of the most brutal subversions of this, in Star Trek: The Next Generation, the completely altered Jean-Luc Picard, aka Locutus, addresses the Enterprise crew after their failed attempt to destroy him. "Your resistance is hopeless... Number One." The look on Riker's face, and the crew's, was pure Oh Shit!!. The Reveal here is that Locutus - and therefore the Borg - had access to all Picard's memories, and therefore knew all the Federation's plans to try and defeat the Borg.
- Played straight in the episode "Schizoid Man", where Picard is satisfied that Data has shaken off Ira Graves's attempt at Brain Uploading because Data has returned to his normal, slightly-too-precise philosophy.
- In Star Trek: Deep Space Nine, a hostile changeling takes on the form of Odo, knowing it's the one thing the Defiant crew can't test for. As the identical changelings face off, each one tries to tell O'Brien something that presumably only the real Odo would know. O'Brien subverts the trope by quickly putting a stop to the whole thing.
O'Brien: I've got more important things to do than play "choose the changeling"! (To his assistant) Keep the phaser on both of them.
- A lighter Deep Space Nine example comes in the episode "Children of Time", when an alternate-future Dax host suggests he could do this to prove that he really is Dax, and proceeds to recount one of Curzon's memories of Sisko...one that Sisko clearly doesn't care to remember.
Yedrin Dax: Do you remember that dancer that you met on Pelios station? The one who...
Sisko: (interrupting) The one who — that'll do. Thank you.
- A lighter Deep Space Nine example comes in the episode "Children of Time", when an alternate-future Dax host suggests he could do this to prove that he really is Dax, and proceeds to recount one of Curzon's memories of Sisko...one that Sisko clearly doesn't care to remember.
- Inverted by the Creator/CBBC series Stupid. In one episode, King Stupid and his gremlin butler Goober plan to get rid of Stupids Evil Twin, Count Cruel by sending him to the real world. Unfortunately, Cruel overhears the plan, and dresses as Stupid. After a bit of back and forth between them, one of them then promises Goober a day off if hes spared, causing Goober to fire the teleportation beam at him, as the real King Stupid would never give Goober a day off, even if his life depended on it.
- In Switched, there's a physical variant — as opposed to spoken dialogue — during the climax where the four teens confront each other. Umine's mother appears off-screen and yells her daughter's name. Ayumi-as-Umine responds to the yell, but Umine-as-Ayumi is immediately terrified and looks right at her mother, who then says "I didn't believe it until seeing your face."
- In Terminator: The Sarah Connor Chronicles, being a Terminator Spin-Off, "come with me if you want to live" is how Cameron identifies herself to John.
- It also helps that he has seen her shot a minute ago.
- A storyline on Third Watch had the cops are searching for a pair of rapists who pose as police officers so that they can pull women over and then assault them. At the episodes end, as the fake cops are menacing a woman, the real cops arrive. The fake cops try to claim that the woman's screams for help are just the raving of someone high on drugs. Already suspicious (they know the woman and know she's not an addict), one of the real cops asks the fakers a question in "cop lingo". When he's unable to answer, they instantly know they've caught the criminals.
- An episode of Touched by an Angel had a local politician's longtime friend, a high school teacher, being accused of statutory rape. She believed his vehement denials due to their friendship and that she had overheard the girl vowing "to get back at him" for a poor grade. To that end, she obtained a copy of the girl's complaint... and was shocked to realize that the girl was telling the truth. How? She quoted, word for word, the same cheesy seduction lines that the man had used on her 20 years prior.
- The Twilight Zone (1985): In "Shatterday", Peter Jay Novins tests his alter ego's claim to be him by asking him what his childhood friend Skip Fisher's father did for a living. He correctly answers that he was a fireman until he quit his job to work at a Studebaker dealership.
- The main plot of the The West Wing episode "Shibboleth" was around whether the Bartlet Administration should grant asylum to a group of stowaway Chinese found in a ship container; they claimed to be Christians being persecuted by the Chinese government, but among the myriad array of political pressures from both Christian groups and the Chinese government (trade talks were on the horizon) there were also questions as to whether their professed faith was genuine as there had been previous instances of stowaways being coached into saying that. Bartlet has a one-on-one meeting with one of the refugees who can speak English and begins by asking him to list the Apostles; the refugee answers correctly but points out that being a Christian wasn't about memorizing historical figures but rather that "faith was the true shibboleth". Bartlet, himself a devout Catholic and who had previously used that same expression, determines from that response that they were truly Christians and arranges a way for them to remain in the United States by having the California National Guard, who was guarding them to this point, stand down and allow the refugees to escape custody — this would both let the refugees go free while also give the Chinese government a face-saving excuse to avoid jeopardizing the upcoming trade talks.
- In an episode of Wings, Brian is caught in a bank robbery and hears the masked robber use the unusual phrase, "We'll all be sitting in butter!" Later, as he flies an unknown client back to the mainland, the client uses the same phrase, cluing Brian in to the fact that he's transporting the robber.
- In the Without a Trace episode "Suspect", the agents believe that the Victim of the Week has been abducted by the headmaster of his school. When one of them questions another student, the boy tells him, "He was going to invite him over to his house for a barbecue, then tell him that it was cancelled, then invite him to stay for a drink. . ." The agent instantly realizes that there's only one way that he could know that and gently asks him, "Did he do that to you?", which the kid confirms.
- Wizards of Waverly Place: When the Russos create duplicates of themselves to escape the government agent, Professor Crumbs recognizes the real Alex when she tells him that his beard stinks.
- The X-Files
- In the critically acclaimed episode "Beyond the Sea", the psychic death row inmate (although whether his abilities are real or not is made deliberately ambiguous) freaks out Dana Scully a lot by referring to her by a nickname only her recently-deceased father calls her.
- Also, in the two-part episode "Dreamland", in which Mulder switches bodies with an Area 51 worker. He tries to convince Scully that it's really him by rattling off some of her personal information. She is not impressed.
Mulder (as Morris): I'm Mulder. I'm really Mulder. I switched bodies, places, identities with this man Morris Fletcher, the man that you think is Mulder, but he's not. Of course you don't believe me. Why was I expecting anything different? Your full name is Dana Katherine Scully. Your badge number is... Hell! I don't know your badge number. Your mother's name is Margaret. Your brother's name is Bill Jr. He's in the Navy and he hates me. Lately, for lunch, you've been having this six-ounce cup of yogurt, plain yogurt, into which you stir some bee pollen because you're on some kind of a bee pollen kick even though I tell you you're a scientist and you should know better.
Scully: Look... Any of that information could have been gathered by anyone.
Mulder (as Morris): Even that yogurt thing? That is so you. That is so Scully. Well, it's good to know you haven't changed. That's somewhat comforting.
- In the Young Blades episode "The Chameleon", after Captain Duval gets himself thrown in jail and the Musketeers believe he is a shapeshifter trying to frame Duval:
Siroc: If you're the real Captain Duval, tell us something only he would know.
Duval: Like what?
D'Artagnan: Like what we got you for your last birthday.
Duval: Nothing. Bunch of thoughtless, shiftless recruits.
Siroc: Yeah, that's the Captain.
- In Brad Paisley's "Letter to Me", he says that if he could send a letter back to himself when he was still in high school, he'd prove to his past self it was really him by telling him to look under the bed for the Skoal (chewing tobacco) can and Playboy no one else knew he had.
- It's believed that the Japanese custom of answering the phone with "moshimoshi?" was to affirm the speaker as human. Supposedly, Kitsune would be unable to pronounce that phrase.
- Older Than Feudalism: In The Four Gospels, after Jesus comes Back from the Dead, not all of his disciples recognize him right away. On one occasion related by Luke, he walks and talks with two of them all the way from Jerusalem to Emmaus, and they don't realize who they are talking with until he prays before a meal — apparently, the prayer was something only he would say. (Then, as soon as they recognize him, he disappears.)
- Based on the context, the words in question were most likely, "This is My Body."
- Luke specifically says that Jesus gave thanks and broke the bread, which is how he described what happened before he said "This is my body" at the Last Supper, so a common interpretation is that the way Jesus broke the bread was distinctive.
- In Red Panda Adventures, when the Flying Squirrel is hypnotized to believe that the enemy they're fighting is the Red Panda and the Red Panda is the bad guy, the Panda proves his identity by whispering "Kit Baxter, behave yourself!" in her ear.
- In Dawn of a New Age: Oldport Blues, Ivy comes across her best friend Luna while the latter is being imbued with her superpower and spouting electricity from every orifice. Convinced that she's some monstrous imposter, Ivy runs away. Luna catches up to her, and Ivy realises that she's the real Luna when she bluntly tells Ivy to 'nut up and stop being a pussy'.
- In Final Fantasy VI, King Edgar takes charge of a band of thieves under the rather transparent anagram "Gerad." In the SNES translation, Celes claims it can't be anyone but Edgar when he refers to her as "My lady", though the fact that "Gerad"'s clothes are just brown versions of Edgar's royal blues didn't exactly help to keep his identity secret either. Made more obvious in Japanese, since Edgar explicitly uses the English word "lady" both normally and in disguise. Rather than a slipup as the Woolsey localization would suggest, it is implied he is intentionally giving clues to Celes and Sabin.
- In Metroid Fusion, Samus (and the player) gets tipped off that the AI she named after her old commanding officer from her army days, Adam Malkovich, really is said officer when, after giving her an order, it asks, "Any objections, Lady?" - something her commanding officer always said after giving her a briefing.
- That line was used again in the trailer for Metroid: Other M as a cue to the audience regarding what game Nintendo was announcing, as the scenes depicted up to that point weren't obviously from a Metroid game.
- In Other M itself, Samus recognizes Anthony Higgs when he calls her "Princess" near the start of the game, and at the end.
- Metroid Dread makes Adam's catchphrase a subtle clue of something being wrong. Outside of the opening cutscene, Adam never addresses Samus as "Lady" and later starts addressing her by her full name. The "Adam" Samus was speaking to throughout her adventure was actually Raven Beak impersonating Adam.
- Riku identifies Roxas as Sora's Nobody this way in Kingdom Hearts: 358/2 Days. After the two have a skirmish, he says "Come on Sora, I thought you were stronger than that." Without thinking, Roxas replies "Get real! Look which one of us is winning!", and immediately wonders why he said it, while Riku realizes that his opponent is "his Nobody".
- In Digimon World 2, at some point late in the game, a member of the Blood Knights, Commander Damien, disguises himself as a Black Sword cadet. Your character gets suspicious, and in an attempt to draw him out, calls out "Commander Damien, sir!". Damien responds, but not long before he realizes he just blew his cover.
- Quarians in Mass Effect are taught a certain phrase to use when returning to the Flotilla, as they usually arrive on a different ship than the one they left on. If they don't provide that phrase when prompted, then the Flotilla knows that they're returning under duress, and their ship is destroyed. They even have a separate phrase that sounds right if you're not in the know, but signals the Flotilla that something is wrong. It's also a strong signifier of the quarian sense of communal duty, since it also means that the ship they are on will be destroyed.
- Another example occurs when, if you gave Tali the geth data during her personal mission in the first game, you can use it to prove it's really you when you meet her again in the second.
- Played with in the Dawn of War II: Chaos Rising campaign, in which one of six characters performs a FaceHeel Turn depending on their Corruption level. If Tarkus is revealed as the traitor he spends the mission giving his former Battle Brothers advice and quoting the Codex Astartes, which infuriates them, because no traitor is worthy to do such things.
- Played with in Super Paper Mario, where the player must determine who the real Merlee is in one chapter thanks to a shapeshifting villain. A game show is hosted, where the player can ask five questions, then choose afterwards. However, the actual way to figure this out is that the real Merlee has a fly buzzing around her, since she spent half the chapter hiding in a toilet in a public restroom.
- Swaine in Ni no Kuni has a habit of referring to his group of friends as "You lot"—"Stand back, you lot!" "Let's do this, you lot!" So when the party travels to the past, and the young Prince Gascon refers to them as "you lot," it immediately raises some suspicions...
- A Hat in Time:
- Played with in an early version's mission where Hat Kid must convince a group of Mafia goons that she's really a friend of theirs named Geoffrey. Geoffrey, as it happens, is known to be a complete Jerkass. So if you do something incredibly jerkish to them, they'll accept her as Geoffrey, regardless of the fact that she's a tiny little girl and not a hulking Mafia goon.
- In the final game, after completing Chapter 2 (supposedly), Hat Kid receives a call on her ship's phone from the same voice that kept calling the train phones in "Murder on the Owl Express". They end the call by revealing themselves as the loser of the Battle of the Birds, by referring to Hat Kid as either "lassie" (the Conductor's nickname for her) or "darling" (DJ Groove's nickname for her).
- In Dragon Quest VI, the chancellor of Somnia (who's effectively taken over the kingdom) uses this to get you thrown out - he asks the hero, who is being taken for the Prince of Somnia, the name of his late sister. None of the options you're given are correct, and he denounces you as an imposter. Subverted in that the hero is the Prince, but all his memories are tied up with his real body, which is on the other side of the continent right now.
- In Grand Theft Auto V, Michael de Santa says his signature line "You forget thousands of things every day. How bout you make sure this is one of them." This comes back to bite him in the ass when his old partner-in-crime Trevor recognizes the phrase and tracks him down.
- In the ending where Alex Mason survives the events of "Suffer With Me" in Call of Duty: Black Ops II, Woods gets a visitor and tries to tell him not to enter. It turns out to be Alex, greeting him by telling Woods he looks like hammered shit.
- Used as The Reveal in Blazblue. A lot of people suspected that the real identity of Hakumen was that of psycho Jin Kisaragi through faint breadcrumbs, but the real kicker that clued in most people was in the second game, when he says a slightly less elaborate version of Hakumen's famous Badass Creed when fighting Tsubaki Yayoi and at the same time for the first time successfully resisting the effects of his Nox Nyctores through his will:
"I am the cold steel! The blade that will restore balance to this world! Nox Nyctrories Yukianesa, activate!"
- A villainous example from Bravely Second: Anne the fairy, advisor to Kaiser Oblivion, addresses the player, reprising her lines from the opening of the first game and revealing that she is Airy's sister.
- Anne Oh, hello. I see fire in those eyes! How do I put it? They've a strong sense of duty. Like whatever you start, you'll always see through, no matter what!
- In Hyperdimension Neptunia Re;Birth1, in order to tell which of two Blancs are the real one, the heroes start asking questions supposedly only the real Blanc knows the answer to. However, they're all embarrassing questions about things such as her measurements and her novels. The fake one answers them perfectly and calmly, but everyone immediately points out the real one when she angrily snaps from all her secrets being publicly revealed because everyone knows Blanc has a Hair-Trigger Temper and swears a lot during it.
- In Cadenza 4: Fame, Theft and Murder Michael, who's a victim of Grand Theft Me, convinces Big Jim it's really him by singing a line of a song he wrote for Jim's birthday.
- In one of the climaxes of Detroit: Become Human, Connor if he becomes Deviant gets put into this situation when he fights another non-Deviant version of himself and Hank tries to guess out the false one by asking them what his son's name is. This can become problematic since it is completely possible to miss out on the options that reveal the name of Hank's son, essentially forcing players to take a guess or to already know.
- In one sidequest in Assassin's Creed: Odyssey, you confront a villainous priestess and her identical, non-evil twin. You can ask them questions, but they both have all the right answers. The proper way to solve the dilemma is to notice that one of them uses a habitual phrase and call her out on it. The cheap way to solve it is to use your eagle vision.
- Ace Combat Zero: The Belkan War gives us Pixy's catchphrase "yo buddy, you still alive?", which he'll ask you at several points after particularly hard missions. After he defects and disappears, your base gets bombed by a giant flying battleship and you track and shoot it down, you receive an encrypted message, which turns out to be Pixy's catchphrase, hinting that he has something to do with the attack. He turns out to be the Final Boss and the ultimate leader of A World With No Boundaries.
- String Tyrant A transformed Mary can use this to transform Lauren peacefully by talking to him, the same for Jessie but only if she declared her love
- The final memory for the "Champions' Ballad" DLC of The Legend of Zelda: Breath of the Wild features the Champions having their picture taken by an offscreen character who hasn't spoken in any of the game's other voiced cutscenes. While they're never directly identified, the fact that their final line is "Click, Snap!" makes it clear that it's Purah.
- Hyrule Warriors: Age of Calamity: When Urbosa saves Zelda from an impostor, she makes a point of calling her by the nickname "Little Bird", which the impostor had failed to do.
- In Dominic Deegan: Oracle for Hire, Gregory is disguised as "ace reporter Buzz Beardman"... but Rachel recognizes him right away when she hears the name, because Gregory created Buzz Beardman as a character in a comic book he made as a child.
- Klo Tark's spirit identifies himself by mentioning "he who I would call my brother", his last words as a living person, to Dominic, the person he was referring to with said last words.
- In The Order of the Stick 397, Nale identifies himself as the Evil Twin by responding characteristically to an insult directed at his Evil Plans.
- This same trait is later used in an inversion of this trope: Part of Tarquin's evidence that Elan is not Nale is that Elan did not ramble about his intellectual superiority, which Nale would have done.
- Subverted the first time Vaarsuvius's familiar, Blackwing, speaks to Roy and Belkar.
Belkar: It can talk?!?
Roy: No, probably not. I think it's probably some sort of magical message [...]. Those were V's words, just coming out of the bird's beak.
Blackwing: You are both ignorant cretins.
Belkar: Yeah. I guess you're right.
- Inverted in another instance. When Roy is fighting the Vampire Durkon his opponent taunts him over his younger brother's death, even asking how many pieces the body was in. This is so uncharacteristic of Durkon that Roy realizes that Durkon either suffered a Death of Personality upon becoming a vampire or is suffering Demonic Possession.
- Bob and George: Don't say "What?" in response to your name if you want to go for Implausible Deniability.
- In Sluggy Freelance, not so much Something Only They Would Say as Something Only They Would Do. Upon his return from an alternate dimension, Torg hugs Bun-Bun. This results in the inevitable beating. At first, the other characters think this proves he isn't their Torg, since their Torg would've known Bun-Bun would beat him up over that. However, they then realize it was their Torg because he seems happy about getting beaten up, and only he would do something so stupid as use Bun-Bun's aggression to determine whether he's in the right dimension or not.
- In this xkcd strip, someone discovers that babbling enthusiastically about foolproof ways to establish his identity is apparently sufficient to establish his identity.
- The Alt text makes it even better:
"Not sure why I just taught everyone to flawlessly impersonate me to pretty much anyone I know. Just remember to constantly bring up how cool it is that birds are dinosaurs and you'll be set."
- The Alt text makes it even better:
- Girl Genius: Higgs is questioning the identity of the fragment of the Castle stuck in dingbot form up until it gleefuly orders him to murder Tarvek.
Tarvek: You'll notice it's got every bit of the castle's usual charm.
Castle: Now, that is certainly true! General? Kill him and let's be off.
Higgs: Yep. That's the castle.
- In Gunnerkrigg Court, the Annie who spoke to Loup convinces Winsbury and Janet she's real because she knows they're a couple. At this point, all the evidence suggests both Annies are real, though, or least until a weird flame spirit thing tells them both of them are in the wrong timeline, so there likely is another Annie somewhere.
- The trope is subverted in the Housepets! storyline "My Life as a Teenage Squirrel", when Marion, a male human teenager who woke up as a female squirrel is trying to explain this to his girlfriend, she asks if she's expected to believe this, and he says no, it's utterly unbelievable and nothing he can do or say could prove it. She suggests telling her something only Marion would know, and he describes what was clearly the most embarrassing experience of his life. However, the logically-minded Lois still finds the very idea of such a transformation so unbelievable that she immediately jumps to a more "rational" conclusion instead.
Lois: Marion told you about that.Marion: You see?!
- Marion gets his revenge later on, by popping this same question when Lois has been transformed into a bobcat herself, right before Marion's eyes.
Lois: I swear I will eat you.
- Marion gets his revenge later on, by popping this same question when Lois has been transformed into a bobcat herself, right before Marion's eyes.
- Out-of-Placers has Kass undergo a Baleful Polymorph early on. Resident 'medic' Galen doesn't buy it until he's roundly and articulately insulted by the now-yinglet Kass.
Galen: What, that's Kass? No it isn't. Quit being stupid.
Kass: Galen, you are a pazetic smoke-spitting loser who hasn't done any real medical work since za war and I wouldn't let you help me even if you could. You ass.
Galen: Holy shit! Kass! Whadda they done to ya!?
- Saturday Morning Breakfast Cereal: Parodied here when a man proves to his wife that he is her real husband by pointing out the acne on her butt. She guns him down and and takes the robot as her husband.
- In the Paradise setting, a number of people who have been involuntarily Changed into Funny Animals use this method to convince friends and loved ones that it's "really them".
- In Qwerpline Derek's voice changes and Alex asks him a series of questions (over the phone) to try and confirm his identity. The fact that Derek completely fails to answer any of the questions convinces Alex that it's actually him.
Alex: "Tell me what Gus' new tattoo say?"
Derek: "I don't know, I can't read Japanese."
Alex: "Oooh, Okay, Possible Derek. How many nipples does Michael O'Leary have?"
Michael: "The answer, gentle listener, may surprise you."
Derek: "Oh come on! Everybody knows that! He won the contest!"
Alex: "Okay... How about this: What does the poster in the recording studio say?"
Derek: "That's a dirty trick! You know I can't say those 8 words on radio!"
Alex: "AAAAAH! IT'S DEREK!"
- The concept of the shibboleth, a way of identifying someone as an ally as described in the Book of Judges, where captured Ephraimites are betrayed by the fact that they can't pronunce the "sh" phoneme and would say "sibboleth" instead, is based around this. These days, shibboleths are call-and-response; a belligerent in a war will have a certain phrase and counter-phrase. If an approaching battalion gets the phrase wrong, they're the enemy. If the guard gets the counter-phrase wrong, the outpost is under enemy control. Examples include:
- During the invasion of Normandy, the Americans would open with "Flash," counter with "Thunder," and confirm with "Welcome." This hinges on the fact that a German would pronounce it "Velcome," and caused problems for some German paratroopers that defected, as well as some German- and Yiddish-speaking Jews who had fled German rule and joined the US Army.
- A British variant in the invasion summer of 1940 would have been, for the same reasons, constructed like Weymouth War Weapons Week
- American POWs in Vietnam communicated by tapping Morse code on their cell walls. One would initiate a conversation by tapping the familiar "Shave And A Haircut" pattern, and the other would finish with "two bits". If the respondent instead repeated "shave and a haircut", it meant he was a Vietnamese agent.
- When Americans were being evacuated from Saigon, American newsman Ken Kashiwahara was afraid of being mistaken as Vietnamese and left behind, so he planned to say "I'm from Los Angeles, and the Dodgers won the pennant" if that happened (it didn't).
- English rioters during the Peasants' Revolt went around looking for Flemish weavers to beat up, identifying them by demanding people say "bread and cheese", which the Flemings did with a distinctive accent.
- About eighty years previously, the Flemish used "Schild en Vriend" (shield and friend), which the French who they were revolting against could not pronounce, making it Scilt, so the Flemish knew who to butcher.
- Sectarian fighters in Northern Ireland can supposedly identify whether someone is a Catholic or a Protestant depending on how they pronounce the letter H (Protestants would call it aitch while Catholics would call it haich).
- Shibboleths need not be confined to wartime or otherwise violent situations. A lot of Swiss people have a habit of making any and all foreigners say 'Chochichäschtli' (a small kitchen cupboard). Not only is it rather difficult to get all these 'ch' sounds right, even if people do, they usually have trouble pronouncing the vowels the correct way. However, if someone is Welsh or Scottish, they usually manage pretty well.
- Unexpected pronunciations of local place names can out someone as not being from the area, even if accent isn't an issue.
- If you're in New York City and don't want to be identified as a tourist, don't pronounce Houston Street like the city in Texas. Pronounce it like "HOUSE-ten" - the street name is a corruption of William Houstoun, who represented Georgia at both the Continental Congress and the US Constitutional Convention (the street used to be part of his father-in-law's estate).
- Natives of Austin, Texas can usually tell if someone is new to the city (or a tourist) by how they pronounce Manchaca note Road.
- It's easy to tell who has spent some time in the state of Hawaii in both verbal and written ways. When it comes to the written form, it's people who are diligent about including the ʻokina in applicable words, given that the ʻokina is considered part of the Hawaiian alphabet, meaning that the state is properly spelled "Hawaiʻi". Verbally, they account for the glottal stop the ʻokina represents (similar to the way "tt" is pronounced in a Cockney pronunciation of the word "bottle"), and they pronounce Ws as Vs in Hawaiian words. So, where the normal person would say "huh-WHY-yee", the native or longtime resident would say "ha-VAH-ee".
- A few examples from the Pacific Northwest: Oregon (locals pronounce it "OR-uh-gun", not "OR-uh-gone"), Willamette ("wa-LAM-et", leading to the rhyme "Willamette, dammit!"), and Couch Street ("Cooch Street"). Pronouncing any of those wrong is a dead giveaway that you're not a local.
- FBI turncoat Robert Hanssen was caught this way. After several US agents had been captured and executed by the Soviets, the Bureau knew they had a mole on their hands. No one suspected Hanssen, however. He was even tasked with finding the leaks for a time. Eventually a communique between Hanssen and his handlers was intercepted, but there was no way to tell who the mole was —until an agent recognized a racial slur the mole made as something only Hanssen would say.note
- Former dictator of the Dominican Republic Rafael Trujillo decided that he didn't want any Haitians in his country (the Dominican Republic and Haiti share the island of Hispaniola). So, he had his agents show parsley to people near the border and ask them what it was. The Spanish speaking Dominicans would be able to pronounce the Spanish word 'perejil' ('parsley') properly, while French speaking Haitians would not. Those who couldn't were usually killed and it's estimated that there were between 20,000 and 30,000 deaths in the "Parsley Massacre".
- A Finnish shibboleth during the WWII was Höyryjyrä ("steamroller"). The voiced 'h', frontal 'ö' and 'ä' phonems, labial 'y' and rolling 'r' are almost impossible for anyone except native Finns to pronounce.
- Likewise, the name of the town of Jyväskylä would be nigh impossible for anyone but a native Finn to pronounce.
- One test used by Americans during WWII to tell if someone was a Japanese spy was to ask them to say the word 'Lollapalooza'. The trouble native Japanese have with the letter L was used to good advantage.
- An Australian accent can be difficult to reproduce without practice, so if you really wanted to know if someone is from Down Under, asking them a simple question, like to say 'How are you going' can often reveal them, as they will most like say something along the lines of 'How ya garn'. And if you ever ran into someone with a great fake Aussie accent, getting a genuine Aussie to check the slang (even small ones like mate, arvo [afternoon], servo [service station] or other slang words) they use.
- Ted Kaczynski was exposed as the Unabomber by his brother David when the latter read the Unabomber Manifesto and found not only similar themes to an essay Ted wrote in college but also the sentence "You can't eat your cake and have it, too" as opposed to the usual idiom "You can't have your cake and eat it too". David had only ever heard that alternate phrasing used by Ted and his mother.
- Want to know if someone's from Chicago? Just ask them if it's "Too haht for hackey."
- If you are in a social network and you suspect that a user is a Spaniard or Latin American and they are pretending to be from another country, call them "Spanish", if they answer back with "I am not Spanish", they will prove that they are, in fact, Hispanic. Few Hispanics or Latinos know that the demonym for those born in Spain is "Spaniard" and not "Spanish".
- Before he died, Harry Houdini promised his wife that he would try to contact her from beyond the grave and set up a secret phrase he would say to verify his identity and counteract frauds. His wife held yearly seances after his death but none of them produced the secret phrase.