Monty Python

BEDEVERE: Tell me, what do you do with witches?
CROWD: Burn, burn them up!
BEDEVERE: And what do you burn apart from witches?
VILLAGER #2: Wood!
BEDEVERE: So, why do witches burn?
VILLAGER #3: B--... 'cause they're made of wood...?
BEDEVERE: Good!
BEDEVERE: So, how do we tell whether she, is made, of wood?
VILLAGER #1: Build a bridge out of her.
BEDEVERE: Aah, but can you not also build bridges out of stone?
VILLAGER #2: Oh, yeah.
BEDEVERE: Does wood sink in water?
VILLAGER #1: No, no.
VILLAGER #2: It floats! It floats!
VILLAGER #1: Throw her into the pond!
BEDEVERE: What also floats in water?
ARTHUR: A duck.
CROWD: Oooh.
BEDEVERE: Exactly! So, logically...,
VILLAGER #1: If... she.. weighs the same as a duck, she's made of wood.
BEDEVERE: And therefore--?
VILLAGER #1: A witch!