Big Disappointment

The teacher asks :
- Jessica, what part of the human body increases ten times when excited ?
Jessica blushes and says :
- That's disgusting, I won't even answer that question.
The teacher calls on Johnny :
- What part of the human body increases ten times when excited ?
- That's easy, says Johnny. It's the pupil of the eye.
- Very good, Johnny, responds the teacher. That's correct.
She then turns to Jessica and says :
- First, you didn't made your homework. Second, you have a dirty mind.
And third, you're in for a big disappointment.