Riddle Trap

The PCs enter a chamber that appears to be a dead end. A Magic Mouth speaks the following riddle:

"Carry me in a bucket and it's lighter than it was."

The answer is "a hole". If any character speaks the answer, a hole opens beneath that character's feet. The hole drops to a pit, a body of water, or some other hazard below. This trap has multiple purposes: occupying the party's time by giving them a puzzle to work out, creating the additional problem of getting the character out of the hole, possibly setting off an alarm, and demonstrating that the place is the product of a perverse mind..