Balto: When Steele returns to Nome, he tells the other dogs that Balto and the sled team died in the blizzard and the medicine was destroyed. He then pulls out Jenna's bandana she'd lent Balto (which Steele tore off in a rage) and tells her that Balto "made [Steele] promise to take care of [her]." Jenna knows Balto would say no such thing, and she immediately sees straight through Steele's Blatant Lies.
Ice Age: Continental Drift: While Manny, Sid, Diego, and Granny are sailing over the night in Captain Gutt's stolen ship trying to return home, they encounter mythical sirens who hypnotize them by shapeshifting into the characters they are in love with (Ellie and Peaches in Manny's case; Shira in Diego's case; a gorgeous female sloth in Sid's case; and a hunk male sloth in Granny's case). Fortunately, Manny snaps out of it when the Ellie-shaped siren tells him he is always right which the real Ellie would never say and immediately changes the direction of the ship saving their skins at the last second.
In the horror/thriller film Assimilate, this is how Kayla realizes her mom is not who she says. She sees her 'mom' after thinking she was dead, and immediately hugs her. Kayla's mom doesn't even attempt to hug her back, which causes Kayla to respond 'You're not my mom' and back away.
In the war film The Big Red One, some German soldiers are posing as Americans. They're found out when somebody notices that throughout their meal they hold the fork in the left hand and the knife in the right instead of cutting off a piece of meat then transferring the fork to the right hand to lift the food to their mouth.
In The Bourne Ultimatum, when Nikki is in a room with Jason Bourne and asked to "code in" on the phone to her superiors. Her personnel record is shown on screen, with responses for "normal" and "under duress", but despite being in a potentially dangerous situation she gives the "normal" response. This was because she'd switched sides. However, she'd already acknowledged that Bourne had been there and there were agents down, so she and Bourne are forced to flee the scene before backup arives.
Bullshot (1983). The dastardly villain, Count Otto von Bruno, who speaks in a stereotypical Prussian accent, fakes the voice of Professor Fenton with Applied Phlebotinum. Despite a chronic malfunction which forces von Bruno to speak at a vastly sped-up rate, the Professor's dim-witted daughter doesn't suspect a thing when he says: "I want you the formula to London bring." Only our hero Bullshot Crummond realises instantly that you'd never hear a split infinitive from an Oxford man, and so it must be a trap!
In Cops And Robbersons, Chevy Chase's character Norman is a huge fan of cop shows and has always dreamed of being a cop (except his ideas of what it means to be a cop come exclusively from TV). After the cops discover that a meeting between criminals is going to take place next door to his house, detectives Jake and Tony set up a stakeout in Norman's house, much to his delight. Jake is initially annoyed at Norman's assumptions about cops, especially when Norman interferes in Jack's duties. However, when the bad guys take Norman's family hostage, Norman calls his own house (not knowing the situation), and Jake tells him a message involving time. Norman is confused, but then looks up police codes and figures out that there's a hostage situation at his house. Unfortunately, instead of calling the police like Jake wanted, Norman decides to rescue them himself.
In Die Hard with a Vengeance, a bunch of German mercenaries impersonate cops. Although the leader speaks English with a flawless American accent, he slips up on a few word choices, such as calling an elevator a "lift" and saying that it's raining "dogs and cats", instead of the usual "cats and dogs". When McClane recognizes that one of them is wearing a friend's badge, and mentions the lottery to figure out if anyone on the elevator is real. None of the fake cops know last night's numbers, though in the beginning it's established that every NYPD cop plays the lottery and knows exactly what the winning numbers were.
In Even Lambs Have Teeth, Jason gets suspicious when one of the kidnappers sends a text purporting to be from Katie, but neglects to change the codeword at the end of the message.
In From Russia with Love, James Bond chastises himself for not recognising an enemy agent posing as a British gentleman spy when the man orders the wrong wine with a fish course at dinner. Unfortunately, Bond only realises this hideous faux pas after the enemy has him at gunpoint.
Holmes & Watson: When Holmes finds the crumbs of Mrs Hudson's cake on Watson's plate, he realises that Watson is trying to send him a message, as Watson would never have left crumbs of his favourite cake behind otherwise.
In It Could Happen to You: When a cop walks into a local deli to get coffee, he asks where the owner's wife is. The owner tells him that she's out sick, but as he turns to get supplies we see that his wife is being held at gunpoint by a robber. Knowing that the cop can't see this, he then gives him the coffee for free. Sure enough, when the cop he goes outside to join his partner, he tells him that the man is being robbed — aside from the free coffee, having come to the store for years, they know that "that bitch would show up for work even if she were dead".
In Jack Reacher, when Reacher investigates the shootings apparently committed by James Barr, he soon establishes a problem; Barr was a competent shooter, but not to the insane degree the killings demanded, and an important part of sniper training isn't just aiming and firing, but choosing where to shoot from, as the optimal firing position wouldn't have left any of the Orgy of Evidence. The shootings were committed from a parking garage where the shooter would have had the sun in his eyes while his targets were moving left and right, but he could have had a better shooting position from a nearby highway bridge that would have put the sun behind him and his targets virtually in single file, allowing him to shoot from a van without leaving shell casings or other evidence; from this, Reacher determines that Barr was framed.
In the second Lara Croft: Tomb Raider movie, Lara's butler tries to do this, but is rebuked for it. "Why are we even having this conversation?"
In Mario (1984), Simon is always shirking his duties at his mother's grocery store to spend time with Mario or Hélène. When he suddenly turns into a workaholic after Hélène leaves the island, his mother knows something's wrong.
In the second Miss Congeniality movie, Miss United States drops a big hint to her location by saying "My booty is on the line here." Sandra's character catches on and explains that "She would never refer to her butt as her booty... she would never refer to her butt as her butt! She calls it a po-po!" The kidnappers tie her and the celebrity pageant host into the sinking ship at Treasure Island in Las Vegas to passively kill them.
Mortal Kombat: During the final showdown, Shang Tsung pulls a Shapeshifter Guilt Trip against Liu Kang by morphing into his brother Chan, who Shang Tsung had murdered. Though Liu knows it's not the real Chan (after all, Shang morphed right in front of him), he's still hesitant to attack until Shang!Chan says he forgives Liu for letting him die. Though Liu blames himself for Chan's death, he knows that Chan himself wouldn't... and hearing this gives him the right state of mind of who's really to blame:
Liu Kang: No....it wasn't my fault! Chan chose his own path...every man is responsible for his own destiny. Shang Tsung killed my brother!
The trap is somewhat different. Mitch Wilkinson forces Emily Appleton to give her ex-husband a rather unconvincing fake translation of some Olmec hieroglyphs. He doesn't seem to pick up on her gestures, so she promptly texts her son Ben Gates the real translation.
She also deliberately starts a fight with her ex-husband, mentioning a place seemingly from their past. Except it's a subtle historical reference that only her ex-husband and son (and her son's ex-girlfriend) could figure out.
The film adaptation of Night of the Fox (1986) has Field Marshall Erwin Rommel meeting with generals plotting against Hitler. To give himself the perfect cover, Rommel enlists Erich Berger, a corporal who is a stunning lookalike to pose as Rommel for a visit to the Jersey Islands. Also there is Harry Martineau, an OSS agent posing as an SS officer on a secret assignment. Harry decides to kill "Rommel" to hurt the German war effort. He confronts him in private with Berger babbling he's not Rommel and even tearing his wig off. Harry just seems disappointed as "I expected better from you." He's about to pull the trigger when Berger starts praying...in Hebrew. It turns out the real Berger was killed in a bombing three years earlier and his body was found by Jewish actor Heini Baum. Seeing Berger's call-up papers in his pocket, Baum hit upon the idea that "what better place for a Jew to hide but in the German army?" He and Harry are thus able to use the Rommel masquerade to help each other out.
No Man of Her Own: This happens constantly to Helen as she tries to pretend to be Patricia Harkness: she doesnt know Hugh's (Patricia's husband) favourite song, didnt know that Hugh had a brother (Bill), and signs her real name when trying out a pen out of habit. The Harkness family (who had never met or seen a picture of Patricia) think this is just a result of the train accident, but Bill is the only one that figures out that Patricia isnt really Patricia. But he doesnt care.
In The One I Love, Ethan realizes that the Sophie he's talking to in the guest house isn't his actual wife when she cooks him bacon, because the real Sophie would never let him eat bacon. It's also what tips him off to the fact that the Sophie who escapes with him at the film's end isn't the real one.
In The Ring Two"Aiden" refers to Rachel as "mommy", when he prefers to call his mom by name. This clues her in that he is being possessed.
Screamers. Colonel Hendricksson goes on a mission and discovers the Screamers have taken human form so they can infiltrate their bunkers. When he returns to his own command bunker he calls his Number Two on the radio, telling him to come out and meet him. A voice claiming to be the Number Two answers telling Hendricksson to come inside instead. Hendricksson then asks to speak to Don Giovanni (the opera music he was playing when his character was introduced). When the same voice claiming to be "Don Giovanni" answers, everyone runs like hell.
The Firefly movie, Serenity. Mal and Inara have a polite, awkward conversation by videophone, with Inara inviting Mal to visit her. Discussion with the rest of the crew ensues.
Zoe: So. Trap? Mal:Trap. Kaylee: How do you know Inara don't just wanna see you? People do have feelings. I'm referrin' here to people. Mal: Y'all were watchin' I take it? Zoe: Yes. Mal:You see us fight? Kaylee: No... Mal:[matter-of-factly] Trap.
In Sherlock Holmes: A Game of Shadows, after an action sequence that separates the pair, Mary is understandably confused when Watson sends her a letter saying he doesn't miss her and hopes to never see her again. Mycroft Holmes tells her the truth can be found from a code that he and Sherlock devised as children, where a notice would be taken at face value or as the complete opposite depending on if the first letter of the note was a consonant or a vowel; in this case, Watson's letter is of course the complete opposite of what he means. The letter needed to be coded in case it were intercepted by someone affiliated with Moriarty, who had just targeted Mary in his scheme just to spite Sherlock Holmes.
In Sneakers, Crease draws Brice away from a meeting with the villains in a public meeting space after seeing a newspaper blurb mentioning that the mathematician they had stolen the MacGuffin from has been killed and realizing what their employers really are. He gets Brice to leave with him by holding up the carphone and shouting that it's his mother calling. Since Brice's mother would have no way of calling him, and one of their group has the nickname "Mother", it's a clear signal that he needs to get out of there.
In The Stranger, Franz Kindler (Orson Welles) is an escaped Nazi war criminal living in the United States under a fake identity. He's at a dinner party that also includes Mr. Wilson, a war crimes investigator who suspects that Welles's character might be the missing Kindler. A casual discussion of the German character turns to Karl Marx, which leads Kindler to respond by saying "but Marx wasn't a German; Marx was a Jew." This causes Wilson to realize that "Charles Rankin" is in fact the man he's been hunting.
In the movie Sudden Impact, when Harry gets his usual morning coffee, the café is being robbed; everyone is being forced to act naturally, but the waitress (knowing Harry's usual is "no sugar, no milk") adds lots of sugar-she pours for twenty-five seconds straight. Harry, distracted by some case work he's going over, just pays and leaves with the cup. Outside, he takes a sip, spits it out and turns back to the diner.... then notices "patrons" locking the doors and turning the "Open/Closed" signs around, figures out what's up, and goes around to come in through the back.
In Superman II, the Krypton criminals led by General Zod force their way into the White House. They enter the Oval Office, and ask the person sitting behind the desk to Kneel Before Zod, which he does without saying a word. Immediately, they decide that he is not the President, since someone with that high a rank would put up some resistance.
In SurrogatesBruce Willis' character is tipped off that his partner's surrogate isn't being controlled by his actual partner when she refers to him by his last name. Everybody else in the movie does this, but she always called him Tom.
First when John tries to call his foster parents to warn them about the T-1000:
John: Something's wrong, she's never this nice. [the Terminator takes over] The Terminator:[to John] What's the dog's name? John: Max. The Terminator:[in John's voice]Hey Janelle, what's wrong with Wolfie? I can hear him barking. "Janelle": Wolfie's fine, honey, Wolfie's just fine. Where are you? The Terminator:[hangs up the phone] Your foster parents are dead.
It happens again when the T-1000 takes Sarah Connor's form and asks for help, something the real Sarah had previously berated her son for doing. The other Sarah instead tells John to get out of the way, something the T-1000 would not be inclined to tell his target. In the Director's Cut, however, John is tipped off when he sees his "mother's" foot melting into the floor.
In Thor: The Dark World, a savvy viewer will realize early on that Loki's betrayal of Thor to the Dark Elves is an act. When doing so, he introduces himself as "Loki of Jotunheim". While he actually is a Jotun, he despises his birthplace and his birth parents, and whatever his issues with his adoptive family, he still considers himself to be Asgardian. Without that little hint, Loki's deception is extremely convincing.
In Transcendence, Max quickly begins to suspect something's gone wrong with Will's upload when he's asking for access to financial and educational data almost immediately after he regains his sense of self. The Will he knows was never so proactive, which convinces him that this Will is just an echo superimposed over the PINN AI used as the base for his program. It turns out that Will's actions are entirely in-character, but now he has the means to achieve his goals instead of being content with limited gestures.
In The World's End, Andy realises that Oliver has been replaced when Blank!Oliver doesn't react to a hated childhood nickname, or to to references about Gary having sex with Oliver's sister, Sam.
X-Men: For the audience at least, "Bobby Drake's" stern demeanour when he tells Rogue that she should go is at odds with his introduction as a Nice Guy. As it turns out, Mystique had impersonated him.
X-Men: First Class: How kid Xavier pierces kid Raven's disguise at the beginning of the film. She looks like his mother, but acts nothing like her. He confirms it with telepathy.
X-Men: Days of Future Past: Dr. Bolivar Trask's secretary is surprised when he compliments her scarf, which is something he doesn't normally do. We learn a few seconds later that "Trask" was actually Mystique, who hasn't quite mastered gender roles yet.