From scene 23 of Monty Python and the Holy Grail. No one is allowed to cross the bridge without answering the bridgekeeper's three questions. Eventually, this bridgekeeper was vanquished by the extraordinary wit of King Arthur himself:

BRIDGEKEEPER: Hee hee heh. Stop! What... is your name?
ARTHUR: It is 'Arthur', King of the Britons.
BRIDGEKEEPER: What... is your quest?
ARTHUR: To seek the Holy Grail.
BRIDGEKEEPER: What... is the air-speed velocity of an unladen swallow?
ARTHUR: What do you mean? An African or European swallow?
BRIDGEKEEPER: Huh? I-- I don't know that. Auuuuuuuugh!