Little Johnny- Homework!!

A teacher was reviewing her class's homework assignment.

She asked Susie to stand up and tell the class what part of the human body enlarges to seven times its original size when stimulated. 

Susie stood up, shuffled her feet and said, "Well, I think I know, but I'm too embarrassed to tell you." 

The teacher said, "Sit down, Susie. Johnny, tell the class what part of the human body enlarges to seven times its size when stimulated." 

Johnny said, "That's easy. The pupil of the eye enlarges to seven times its original size when stimulated by light." 

The teacher said, "That's right, Johnny." Then she turned to Susie and said, "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."