Professor: Miss Rogers, what part of the male anatomy may enlarge by a factor of 10 when the male is excited?

Rogers: (Blushing) I... refuse to answer...

Professor: Mr. Smith?

Smith: The iris.

Professor: (coughs) Miss Rogers I can conclude three things. 1. You didn't do the reading last night. 2. Your mind is not where it's supposed to be. 3. You will be disappointed with married life.

(Disclaimer: May not be completely anatomically correct).