This is when somebody has a revelation due to the fact that the person he is talking to has an injury. The most common case of this is secret identities and/or robbers getting injured while masked, and then the person they fought noticing a similar injury on the unmasked person.
This can also happen in a slightly different way. When a person is injured they have to receive medical treatment, it can reveal things they didn't want to be known. The most common one is a soldier being revealed to be a woman.
Or a robot
Often paired with Cut Himself Shaving
, which is the person trying to explain away the odd injury. Even if the explanation is good, it won't fool somebody who knows about the original injury.
Anime and Manga
- Digimon Adventure 02 has Davis play against Ken in a football match where the latter receives a cut to his leg. Later when the Digimon Emperor is seen in the Digital World Davis recognises the cut. Then Ken reveals that he is the Digimon Emperor.
- Dragon Ball Z - Videl points out that the facial scratches Gohan was trying to explain away were pretty much identical to the ones she saw Saiyaman receive when trying to wrangle an escaped dinosaur. She uses this info to blackmail Gohan into teaching her how to fly (She does ask if that's something that can be taught, to her credit).
- This is sort of borderline, but in Magical Girl Lyrical Nanoha Strikers, late in the season, protagonist Subaru fights some combat cyborgs who are kidnapping her big sister Ginga. She fails to save her and is seriously injured, which is when we see that she is a combat cyborg too.
- In A's, Signum declines to take a bath with the others, and after Hayate is out of the room, Zafira correctly guesses that Fate managed to cut through Signum's armor. Signum wanted to prevent Hayate from finding out that they were collecting Linker Cores to save her, as they know that she does not approve of their doing so.
- In one chapter of the Slayers manga, Lina suggests using this to identify a werewolf. Unfortunately, the only injury the werewolf suffered that could be used was that Lina had fireballed it in the ass. Since they couldn't go around town pulling people's pants down, they came up with an alternative plan - they gathered the town's population in one place, fried an egg, and showed them the "Sunny-Side-Up Full Moon". The werewolf exposed himself by being the first to point out how utterly ridiculous this plan was.
- The first criminal to deduce Batman's secret identity (a partner of the Joker called Queenie) did so when she spotted the same shaving nick of the jaw of both Batman and Bruce Wayne.
- Somewhat similar in Batman: The Lost Years, a tie-in comic to Batman: The Animated Series, shows Bruce Wayne playing tennis with Barbara Gordon. He comments on how she favors her left side for her defense, which he realizes is the same advice he gave Batgirl the previous night, and thus figures out her Secret Identity.
- In the first volume of Resident Alien, Harry, an alien masquerading as a human, does not want anyone else to treat his gunshot wound except himself because he's afraid this will happen and people will discover that he's really an alien.
- Spider-Man Trilogy:
- In Batman Returns, Catwoman has to hide the injuries Batman gave her when she's seducing Bruce.
- In X2: X-Men United, Wolverine recognises a disguised Mystique by the claw-marks he gave her in the previous film.
- In Aliens, Bishop is revealed to be an android when he accidentally pierces his skin and "bleeds" a white fluid.
- Subverted in the first Beethoven movie, in which the evil vet fakes an injury after claiming the titular dog attacked him. Later George grabs him by the arm and a moment later realises that there's no injury at all.
- In Prince of Persia: The Sands of Time, Dustan realizes his uncle is the true Big Bad when he notices that his hands are burned from handling the poisoned mantle that killed the Sultan - despite having never touched the robe on screen.
- Averted in the The Green Hornet movie. The titular hero refuses medical attention to the bullet wound in the shoulder he recieved while masked, knowing that it would arouse suspicion if somebody arrived with the same exact injury just after the battle. They decide to fake a drive-by shooting so that he can keep his arm without compromising his identity.
- In Dark Shadows Barnabas catches fire when he is accidentally exposed to sunlight, thus making it obvious to everyone present (including the prospective love interest) that he is a vampire. Try explaining that one to your crush.
- In Return to Cabin by the Lake, a presumed-to-be-dead serial killer named Stanley Caldwell infiltrates a movie set by impersonating one of the producers he murdered. He eventually kidnaps the screenwriter who was doing research into his life, but she initially thinks he's just overdoing a Method Acting approach. He leans over to show her a scar on his arm from a late female victim, leading to the dawning realization that he's the monster she's been looking for.
- A variant: In the Leopold story The Four O'Clock Felon, after one crime goes wrong, the villain switches from armed robbery to breaking & entering. The police finally realize he's the "witness" to that crime, who'd received a leg injury giving him a distinctive limp. He couldn't afford to be seen until the injury healed.
- In the book Juggernaut, not sure if in the movie, the police are searching for Big Bad as he is making his escape. They are searching for a man with a mustache. A cop is about to let a clean shaven man leave when he notices his upper lip is bleeding. Seems he cut himself shaving.
- In Star Trek: New Frontier, Starfleet figures out that Soleta is half-Romulan after she's badly injured after Jumping on a Grenade for her commanding officer. (How, I don't know, given that her other half is Vulcan, and supposedly they're still close enough to each other to interbreed, so...)
- There are several tales in folklore of witches terrorizing a town in animal form, until their paw is wounded by a holy man or witch-hunter, who is then able to find the witch when she resumes human form, because her hand will bear the same wound.
- Echoed in Stephen King's Cycle of the Werewolf. A boy attacked by the werewolf shoots it in the eye with a bottle rocket. Later, he's able to identify the cursed man by the same (unexplained) injury.
- Also used in Women Of The Otherworld. Elena reads a version of the old legend in the Pack's history books: a knight wounded the werewolf's paw, came home to find his own wife bandaging her bloody hand, and killed her. As he gutted her, her unborn wolf cubs fell from her stomach. Overcome with horror, the knight committed suicide. Elena prefers to interpret the belly full of puppies as a metaphor for the knight's guilt when he realized he murdered his wife without letting her explain. In Broken, We learn she's at least half right about the puppies: female werewolves bear their young in human form.
- Parodied in Lords and Ladies:
Weaver: They do say she [Granny Weatherwax] creeps around the place o' nights, as a hare or a bat or something. Changes her shape and all. Not that I believes a word of it but old Weezen over in Slice told me once he shot a hare in the leg one night and next day she passed him on the lane and said "Ouch" and gave him a right ding across the back of his head.
- There's a subtle version of something like this at the end of The Wreck Of The Zephyr, when the limp of the old man narrating the story is juxtaposed with the protagonist of the Framing Story having badly broken his leg at the end.
- A similar one happens in the illustrated children's book Pegasus; the old beggar telling the story ends by saying Pegasus' rider fell off his back mid-flight. He gets up with the help of a walking stick and walks away, dragging one leg.
- The Bloody Chamber uses this in The Werewolf; Little Red Riding Hood takes out the cloth that has a wolf's paw wrapped in it, only for it to fall out as a human hand and reveal her grandmother is the werewolf she fought off earlier.
- A Sweet Valley High book had the girls being courted by twin brothers, one of whom cuts his hand very badly while on a date with Elizabeth. Later, she sees that Jessica's date has a bandaged hand, revealing that there is no twin and that this guy is a jerk who's been playing games with both of them.
- An RL Stine book had a young hospital patient attacked in the shower. Unable to see, she manages to defend herself by cutting her assailant with a razor blade. For several days afterwards, she notices a cut on several people, all of whom provide plausible explanations. She's still fearful and suspicious and not until someone outright tells her that their cut is the result of the razor blade does she know who her attacker is.
- In a Nancy Drew Files book, Nancy is attacked while skiing. Ned comes to her rescue, but the assailant escapes while he's tending to her. But not before Nancy notices that he favors his right leg. Later, while out skiing with one of the resorts instructors, Nancy realizes that she's Alone with the Psycho when she notices that he has the same quirk that her attacker did.
- In Monstrous Regiment there's a story about Sergeant Jackrum that when he was injured he bit the doctor who tried to treat him and then went off to treat himself. Initially this story just seems to highlight Jackrum's badass nature but after the reveal that Jackrum is actually female it becomes clear that he did it to avoid a Revealing Injury.
- In the old Zorro TV serial, Zorro's secret identity was figured out once by the Big Bad of the season. Although there were many Sherlock Holmes-esque clues he cited, they all were just to back up the fact that Don De La Vega had a sword wound in the exact place he had stabbed Zorro.
- The same thing happens in the movie The Mask of Zorro.
- In another episode Zorro himself uses this as a Spot the Imposter trick. Facing both the Alcalde and his impersonator at the same time, he conclusively proves which one is the real Alcalde to all present by pointing out that he had wounded the true Alcalde on the wrist some time previous, then slashing the sleeves of his opponents to see which one had a scar there.
- In an episode of Bones the identity of the Gravedigger is revealed via a rib injury sustained from being hit by a car.
- The cause of many a Robotic Reveal: Data (while suffering amnesia) in one episode of Star Trek: The Next Generation springs to mind.
- Utopia: The only thing anybody knows about Mr Rabbit's identity is the Chinese character for Rabbit carved on his belly. Of course, since nobody has ever seen the scar but knows what it might look like, it's easily forged.
- Robin of Sherwood: The new Robin is shot in the leg, a young nobleman starts to limp. People notice.
- Averted in an episode of Robin Hood. Guy of Gisbourne injures Marian's arm whilst she was in her Night Watchman disguise. Later he casually pats Marian on the arm and notices that she's bleeding. As she's cutting an apple at the time, Marian casually slices her palm with the knife and tells Guy that she accidentally got a little blood on her sleeve. He seems suspicious, but lets it go.
- In an episode of Dr. Quinn, Medicine Woman Sully identifies the leader of the Klu Klux Klan by revealing the burn mark on his arm that he sustained at a rally the night before.
- In an episode of It Takes a Thief (1968), Alexander Mundy gets a slash on the arm from the villain's dragon, and later the villain realizes who his opponent is when he studies photographs and spots that the fake skin on Mundy's arm is wrinkling after it gets wet.
- While not an injury per se, there is an episode of White Collar where Neal gets himself captured and drugged up with an unspecified drug that makes him higher than a kite. When Peter rescues him Neal admits to him that he trusts Peter more than anyone - a revelation he probably wouldn't have made if he weren't so loopy.
- He also admits to stealing some manuscripts via carrier pigeons while in this state.
- In the first episode of Wild Boys, Hogan has a pistol shot out his hand. The troopers later identify Hogan as the bushranger because of the injury to his hand.
- Leverage: In "The Rundown Job", Parker is looking for a bio-terrorist whom she knows has just innoculated himself against the flu virus she is carrying. She walks through the car, bumping each passenger on the arm, until one of them yelps.
- In The Sopranos Tony Blundetto is identified as the killer of Joey Peeps after witnesses claimed Peeps' killer ran away with a limp. Blundetto received the injury when Peeps' car ran over his foot.
- In the B-plot of the Enemy At The Door episode "The Librarian", set on the German-occupied island of Guernsey during World War II, a German officer has been tasked with finding a man who tried to escape the island in the previous episode. The escape attempt happened at night, so the Germans don't have a clear description of the man, but they do know that he was wounded in the arm when a patrol shot at him. After narrowing down the pool of suspects by other means, he manufactures an opportunity to "accidentally" stumble against the arm of his prime suspect, with the suspect's reaction confirming that he has an arm injury which he is concealing.
- The New Avengers: In "To Catch a Rat", Gunnar knows that he will be able to identify the White Rat because he shot the White Rat in the left leg during their last encounter.
- In Tales of Symphonia when Colette takes an attack at the end of the first disk, it damages her sleeve enough to reveal that her "angel toxicosis" is becoming much worse.. The scene plays out rather odd if you are in a new game+ and using a costume title, as they default to the normal costume mid cutscene.
- In the fourth case of Phoenix Wright: Ace Attorney, Manfred Von Karma never had the bullet removed from his shoulder to avoid becoming a suspect in Gregory Edgeworth's death. Phoenix exposes him by first realizing that two bullets were fired (the one that broke the glass and hit von Karma in the shoulder and the one that killed Gregory), and using a metal detector to find the other bullet. Invoked in the third case, when someone steals the Steel Samurai case and pretends to be limping from a sprained ankle to cast suspicion on Will Powers, who sprained his ankle.
- In Apollo Justice: Ace Attorney, the fact that Alita Tiala's scarf hides the marks from where Dr. Meratkis tried to strangle her turns out to be a crucial point of evidence.
- In the first case of Ace Attorney Investigations 2, the president of a foreign country is shot at by someone wearing a red raincoat. Sure enough, a red raincoat happens to be found at the scene, and it has a small bloodstain on the inside. There happens to be a nearby ice cream man named "John Doe" with a bandaged arm that bleeds occasionally, who denies the raincoat is his. There's a twist though: The raincoat is his... but he's not the shooter. There were actually two people wearing red raincoats at the time, and the second one was much more well hidden.
- In Sailor Nothing, Aki is only able to recognize Himei in her Sailor guise because she has a black eye that Aki had noticed earlier in the day.
- Homestuck: Karkat has been hiding the color of his blood for his entire life, so the readers don't learn it until Jack stabs him. In-universe, it's a subversion, though- while Karkat starts freaking out, no one else there actually cares.
- In The Senkari Freijas injury is not plausibly make up as she claims. Of course the fact she gets drunk doesn't help back up her claim in any way...
- In Mulan, the heroine is revealed to be a woman when she saves her commanding officer from death and is injured in the process. Their physician has to patch her up. He tries to be discreet about it, but informs her commanding officer, who is forced to expel her from the army. (Technically he's supposed to kill her, but he still felt gratitude so he let her live.)
- One battle with the Green Goblin in The Spectacular Spider Man leaves the Goblin limping away. Spider-Man follows him and discovers him to be his friend Harry Osborn, complete with Goblin costume and injured leg; while Spidey's suspected culprit, Harry's father Norman, seemed just fine. Subverted next season, when Norman revealed that he really was the Green Goblin all along. He had framed Harry, going so far as to injure his own son's leg to throw Spider-Man off.
- Real Life: Deborah Sampson enlisted as a man in the Continental Army during the American Revolution. She served for a year and a half, including several battles. Deborah came down with malignant fever and was cared for by a doctor, Barnabas Binney. He removed her clothes to treat her and discovered her secret. Dr. Binney later told George Washington, who never uttered a word and honorably discharged Deborah Sampson from the Army at West Point.