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.

An invisible man is here to see you
Nurse: Doctor, there is an invisible man in your waiting room.

Doctor: Tell him I can't see him now. Next.