Completely normal

　　"Would you mind telling me, Doctor," Bob asked, "how you detect a mental deficiency in somebody who appears completely normal?" "Nothing is easier," he replied, "You ask him a simple question which everyone should answer with no trouble. If he hesitates, that puts you on the track." "Well, 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?' " Bob 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."

　　“医生，你能不能告诉我，”鲍勃问，“对于一个看上去很正常的人，你是怎样判断出他有智力缺陷的'呢?”“再没有比这容易的了，”医生回答，“问他一个简单的问题，简单到所有人都知道答案，如果他回答得不干脆，那你就知道是怎么回事了。”“那要问什么样的问题呢?”“嗯，你可以这样问，‘库克船长环球旅行了三次，但是在其中一次的途中他去世了，是哪一次呢?’”鲍勃想了一会儿，紧张的回答道，“你就不能问另外一个问题吗?坦率地说，我对历史了解的不是很多。”