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?”

“That’s easy,” he replied. “You ask them a simple question which everyone should be able to answer with no trouble. If they hesitate, that puts you on the right track.”

“What sort of question would you ask Doctor?”

“Well, you might ask them…”
“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.”
(DOH!)