Professor Higgins at the University of Sydney was giving a lecture on 'Involuntary Muscle Contraction' to his first year medical students.
Realising 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 arsehole is doing while you're having an orgasm?"
She replied: "Probably golfing with his mates".
It took 45 minutes to restore order in the classroom!