A Professor was giving a lecture on "Involuntary Muscular Contractions"
to his first year medical students.

Realizing that 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 fishing with his buddies."

(On topic, too!)