Involuntary Muscular Contractions.... A professor at the University of Mississippi was giving a lecture on "Involuntary Muscular Contractions" to his first year medical students.
Realizing this was not the most riveting subject, the professor decided to lighten the mood slightly.
He pointed to a young woman in the front row and said, "Do you know what your asshole is doing while you're having an orgasm?"
She replied, "Probably deer hunting with his buddies."