A patient in a mental home was firmly convinced that he had swallowed a lightbulb and all the efforts of the team of psychiatrists to convince him otherwise were to no avail.

Finally the chief psychiatrist tried one last trick. He put the patient to bed under heavy sedation and then unscrewed the lightbulb from the bedside lamp. He then laid the bulb carefully on the patient's chest.

Presently the patient came round from the anaesthetic and the psychiatrist said,

`Nothing to worry about now, Mr Smith. We've managed to remove the light-bulb surgically!'

The patient picked the light-bulb up and examined it carefully. Then he looked up and said scornfully,

`You must think I'm stupid! This is a forty-watt plain. The one I swallowed was a hundred-watt pearl!'