Basic Trope: Rooting out an impostor by revealing he doesn't know something he should (or does know something he shouldn't), usually by tricking him into repeating an obvious mistake.
- Straight: Bob gets kidnapped and replaced by a shapeshifter. However, Alice becomes suspicious and offers "Bob" an orange soda, calling it his favorite. Alice knows Bob can't stand orange soda. "Bob" happily accepts the offered soda, confirming Alice's suspicions.
- Exaggerated:
- Bob gets kidnapped and replaced by a shapeshifter. The suspicious Alice offers the shapeshifter an orange soda, calling it his favorite. Bob is a Human Alien with a lethal allergy to orange soda.
- Bob is impersonated by an alien. Alice offers the alien a glass of drain cleaner, who chugs it down without ever considering that it is inedible.
- Downplayed: Bob gets kidnapped and replaced by a shapeshifter. The suspicious Alice offers the shapeshifter an orange soda, saying it's his favorite. His favorite soda is actually cherry cola.
- Justified: Alice wants to figure out if "Bob" is really Bob, without either making a fuss if it's unnecessary or finding out and retaining an element of surprise if it is to get a jump on the imposter when she makes her move.
- Inverted:
- Bob's disguise is exposed when Alice gives him his favorite drink.
- A shapeshifter lures Alice into their trap by impersonating as Bob.
- Subverted:
- The suspicious Alice tells Charlie she'll figure out if "Bob" is really Bob and gets an orange soda, calling it his favorite... And the shapeshifter refuses it, saying she should know he hates orange soda.
- Alice hasn't done her homework. Bob once declined an orange soda, and Alice assumes that Bob hates it.
- Double Subverted: However, then Alice tells him his Aunt Sally wants to talk to him. "Bob" says he'll talk to her later... confirming Alice's suspicions, because Bob's aunt is actually called Sadie.
- Parodied:
- Alice finds out that "Bob" isn't Bob by offering him some dishwashing liquid. Alice knows that Bob hates drinking dishwashing liquid, and so exposes the fake.
- It takes a clever bluff to discern the imposter's identity, even though it was someone wearing a photo of Bob's face over a piece of cardboard.
- Zig Zagged:…Except that they are different aunts, Sadie being Bob's maternal aunt note and Sally being his paternal aunt note . Though the impostor is tricked anyway due to expressing shock, when the real Bob would obviously already know this.
- Averted: There is no impostor.
- Enforced: The author wants a non-verbal way to show Alice has gotten suspicious.
- Lampshaded: "Aha! The real Bob hates orange soda! You're an impostor!"
- Invoked: To prove he's not an impostor, Bob gives intimate details about his life that only he could possibly know.
- Exploited: ???
- Defied: The impersonator studied Bob thoroughly (maybe stealing his memories) to do the ruse.
- Discussed: "I know a good trick to spot an impostor... ask them to answer a question that only the real Bob would know the answer to!"
- Conversed: "Here we go, the 'trip-up-the-impostor' scene."
- Implied: Alice takes an orange soda and goes to talk to "Bob". She comes back later with an empty bottle.Charlie: They got him?Alice: What do you think?
- Played For Laughs: The shapeshifter thinks that their ability to disguise themself is flawless, but they get duped by this trope every single time.
Okay, okay, I'll send you back to the main page; here's the link...Aha! No real troper would have made a mistake like that — they all know the main page is here!
