"Would you mind telling me, Dr. Mark," Joe asked, "how you detect a mental deficiency in somebody who appears completely normal?"
"Nothing is easier," Dr. Mark replied. "You ask him a simple question which everyone 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?'"
Joe thought for 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."
