Medical Students

Two medical students were standing on a street corner watching people as they passed and discussing with each other any abnormalities that they may have seen in passers-by. They saw this old man waddling down the street like a duck at a slow pace.
The two students introduced themselves to the gentleman and told him that they didn't agree with each others diagnosis of the old man's problem. One says, "my friend thinks you have a bad case of haemorrhoids, and I think you have a hernia."
The old man said, "I thought it was a fart, but from the feel of it, it looks like we were all wrong."