This psychiatrist walks into his waiting room and sees two men. One is hanging upside down from the ceiling. The other is sawing an imaginary piece of wood. The doctor approaches the man who is sawing and asks him what he is doing.

'I'm sawing wood,' the man replies.

'And what's your friend doing?' the doctor asks.

'Oh, he thinks he's a light bulb.'

'Well, don't you think you should tell him to get down? The blood is rushing to his head.'

'What, and work in the dark?'