Biology lessons

The 10th grade teacher asks Jessica: "What part of the human body increases to 10 times it's normal size when excited?"

Jessica responds: "That's disgusting! I don't have to answer that question!"

So the teacher asks little Johnny, who responds: "That's easy...the pupil of the eye." "That's correct, Johnny. Very good!"

And turning to Jessica, she says: "i've three things to say to you, young lady... First, you didn't do your homework; second, you have a dirty mind; and third, you're in for a big disappointment!"