Mr. White, the biology teacher at a posh suburban girls' school, asked during class: "Miss Smith, can you name the organ in the human body that, under the appropriate conditions, expands to six times its normal size, and define the conditions."
Miss Smith gasped, then said snottily: "Mr. White, I don't think that is a proper question to ask me. I assure you that my parents will hear of this." With that, she sat down red-faced.
Unperturbed, Mr. White called on Miss Jones, and asked the same question.
Miss Jones, with complete composure, replied: "The pupil of the eye, in dim light."
"Correct," said Mr. White.
"Now, Miss Smith, I have three things to say to you: one, you have not studied your lessons. Two, you have a dirty mind. And three, someday you will be faced with a dreadful disappointment."