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.

Ape Reading List
One day the zoo-keeper noticed that the orangutan was
reading two books -- the Bible and Darwin's Origin of
Species.

In surprise he asked the ape, "Why are you reading both
those books?"

"Well," said the orangutan, "I just wanted to know if I was
my brother's keeper or my keeper's brother."