You've Proven My Point
A noted psychiatrist was a guest at a blonde gathering, and his hostess naturally broached the subject in which the doctor 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," he replied. "You ask a simple question which anyone should answer with no trouble. If he 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 blonde thought a moment, 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."