Yes - it's a woman !!

A professor at the University of Sydney was giving a lecture on
'Involuntary  Muscular Contractions' to his first year medical
students.

  Realizing this was not the most riveting subject, the professor
decided to lighten the mood.

  He pointed to a young woman in the front row and asked:  "Do you
know what your arsehole is doing while you're having an orgasm?"
 

  She replied  "Probably playing golf and drinking beer with his mates."

  It took 16 minutes to restore order in the classroom...