A high-school teacher asks a girl in the class, "What organ of the body enlarges to ten times its normal size during periods of excitement?" The girl stammers and blushes and looks at the floor and says, "I don't want to answer that question."
So the teacher asks a boy, "Do you know the answer?"
The boys answers, "The pupil of the eye."
"That's right," says the teacher. Then he turns to the girl and says, "Two things are obvious. First, you didn't study your lesson last night. Second, you wedding night is going to be a terrible disappointment to you."