Growing Pains

A teacher is reviewing her class' homework assignment. She asks Susie to stand up and tell the class what part of the human body enlarges to seven times its original size when stimulated. Susie stands up, shuffles her feet and says, "Well, I think I know, but I'm too embarrassed to tell you." The teacher says, "Sit down, Susie. Johnny, tell the class what part of the human body enlarges to seven times its size when stimulated." Johnny says, "That's easy. The pupil of the eye enlarges to seven times its original size when stimulated by light." The teacher says, "That's right, Johnny." Then she turns to Susie and says, "Susie, first of all, you didn't do your homework. Second, you have a dirty mind. And third, when you get married, you're in for a big disappointment."