A doctor of psychology at a mental institution was doing his normal
morning rounds, when he entered a patient's room.  He found one
patient sitting on the floor, pretending to saw a piece of wood in
half. 

Another patient was hanging from the ceiling, by his feet. 

The doctor asked the patient on the floor what he was doing.  The
patient replied, "Can't you see I'm sawing this piece of wood in half?" 

Then the doctor asked him what the other patient was doing. 

He said, "Oh, he's my friend, but he's a little crazy.  He thinks he's
a light bulb." 

The doctor looked up at the patient hanging from the ceiling and
noticed his face was flushing red.  The doctor said to the first
patient on the floor: 

"If he is your friend, you should get him down from there before he
hurts himself." 

And the patient said, "What?  And work in the dark?"