Years ago in an old Marvel RPG game, my players were trapped in a computer game by a villain. They came to a bridge guarded by a Black Knight (combining two Holy Grail scenes).
When they approach he calls out, "Before the other side of this bridge you see, must first you answer my questions three. Will you accept my challenge?"
After they respond "yes," he says:
"What is your name?"
"What is your quest?"

Then asks an unanswerable question like the one above. Then blasts the one answering with lightning and repeating the challenge. After getting shocked by lightning about 8 times, one of my players finally realized that they could cross after answering "What is your quest?" since that was the third question.

Good times.