A noted psychiatrist was a guest speaker at an academic function where a prominent politician happened to appear. He took the opportunity to schmooze the good doctor a bit and asked him a question. “Would you mind telling me, Doctor,” he asked, “how you detect a mental deficiency in somebody who appears completely normal?”
“Nothing is easier,” replied the doctor. “You ask a simple question which anyone should answer with no trouble. If the person hesitates, that puts you on the track.”
“What sort of question?” asked the politician.
“Well, you might ask, ‘Captain Cook made three trips around the world and died during one of them. Which one?'”.
The politician thought a moment and then said with a nervous laugh, “You wouldn’t happen to have another example, would you? I must confess, I don’t know much about history.”