Good Thinking

A doctor of psychiatry is doing his normal morning rounds at the hospital when he enters the ward.
He finds Arnold sitting on the floor, pretending to saw a piece of wood in half. Meanwhile Mark is hanging from the ceiling by his feet.
The consultant asks Arnold what he’s doing. Arnold smiles and answers, ‘Can’t you see I’m sawing this piece of wood in half?’
The consultant nods and continues talking to Arnold and ask what Mark is doing on the ceiling. Arnold looks up and murmurs, ‘Oh, he’s my friend, but he’s a little crazy. He thinks he’s a light bulb.’
The consultant looks up and notices that Mark’s face is turning red and blue.
The consultant remonstrates with Arnold and says, ‘If he’s your friend, you should get him down from there before he hurts himself.’
Arnold replies with a sigh, ‘What? And work in the dark.’