A man went into a party and drank some of the punch. He then left early. Everyone at the party who drunk the punch subsequently died of poisoning. Why did the man not die?
The poison from the punch came from the ice cubes. When the man drank the punch, the ice was fully frozen. Gradually, as the ice cubes melted the poison was released into the punch.
What has four legs and a back, but can't walk?