The great psychiatrist was a guest at a very exclusive gathering. His hostess naturally broached the subject with which he was most at ease.
"Would you mind telling me, Doctor," she asked, "how you detect a mental deficiency in somebody who appears completely normal?"
"Nothing is easier," said he. "You ask a simple question which everyone should answer with no trouble. If the person hesitates, that puts you on the track."
"What sort of question?"
"Well, you might ask him, 'Captain Cook made three trips around the world and died during one of them. Which one?' "
The hostess pondered for a moment, then said nervously,
"You wouldn't happen to have another example would you? I must confess I don't know much about sea history ..."