The anatomy instrużctor asks the class "Which is the part of the body which enlarges itself by ten times?" and points at a girl for a reply.
She says " Sir, I know but I am ashamed to tell."
"OK" says the Prof abd points at a boy who replies " The pupil of the eye, Sir."
The Prof says it's correct and turns to the girl again.
"I'll tell you three things my girl. Firstly, you haven't studied your lesson last night."
"Secondly, you have a dirty mind."
"And thirdly, you'll be really disappointed when you get married!"