A professor was giving a lecture on involuntary muscular contractions to his first year medical students.

 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, he decided to lighten the mood. He pointed to a young woman in the front row and asked, "Do you know what your asshole is doing while you're having an orgasm?" She replied, "He's probably playing golf with his friends."