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 asshole is doing  while
you're having an orgasm?"

She replied,  "Probably deer hunting with  his
buddies."