A man phones a mental hospital and asks the receptionist if there is currently anybody in Room 17.
She goes and checks, and comes back to the phone, telling him that the room is vacant.
“thank god,” says the man. “That means I must have really escaped.”
Two metal patient from the same hospital were trying to escape. One says to the other "I'll shine this torch at the top of the wall and you climb up the lightbeam".
"No Way" said the other, "knowing you, you'll switch the torch off when I'm halfway up and I'll fall on my @rse"