Involuntary Muscle Contraction...
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 fishing with his mates.'