Muscular Contractions

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 ass hole is doing while you're having an orgasm?"

She replied,

"Probably deer hunting with his buddies."

The professor laughed so hard he could not continue with the class