Joke.

The Prison Governor was doing his daily morning rounds of the hospital ward, when he came across an inmate sitting on the floor sawing an imaginary piece of wood, while another inmate was dangling from the ceiling by his feet. "What are you doing?" the Governor asked the first inmate. "Can't you see, I'm sawing this piece of wood in half" he replied. "So what's he doing dangling from the ceiling?"  asked the Governor. "Oh he's barmy, he thinks he's a light bulb" said the inmate. "Well he's going red in the face hanging there, don't you think you should tell him to get down before he hurts himself?" replied the Governor. "What and work in the dark?"