A man phones a mental hospital and asks the receptionist...
A man phones a mental hospital and asks the receptionist if there is anybody in room 27. She goes and checks, and comesback to the phone, telling him No, the room is empty. "Good," says the man. "That means I must have really escaped."

Are caterpillars good to eat?
Johnny: Daddy, are caterpillars good to eat?

Father: Have I not told you never to mention such things during meals!

Mother: Why did you say that, Junior? Why did you ask the question?

Johnny: It's because I saw one on daddy's lettuce, but now it's gone.