A group of mental patients was engaged in some therapeutic work in the basement of the institution.

When the superintendent came round, he saw that they were all busy at the carpentry benches and lathes, except for one inmate who was hanging by his ankles from the ceiling.

`What's going on here?' he asked.

`Don't take any notice of him,' said one of the inmates.

`He thinks he's a light-bulb.'

`Well,' said the superintendent with a smile, `I'll soon take care of that. I'll just turn him off!'

He stepped over to the wall switch and one of the other patients shouted,

`Hey, wait a minute! How do you expect us to work in the dark?'