A professer at the University of Sydney was giving a lecture on 'Involuntry Muscular Contractions' to his first year students.
Realising this was not the most riviting subject, the Professer decided to lighten the mood slightly.
He pointed to a young women in the front row and said, 'do u know what your arsehole is doing while u are having an orgasm'
She replied  'most probably fishing with his mates'