Two doctors are in front of their clinic about to go in when they see a man hobbling down the street towards them.
The first doctor says, "I bet that poor chap is suffering from a hernia."
"No no", replies the other doctor, "Clearly he has a knee problem."
When the hobbling man is about to pass them , one of the doctors says, "We have a bet, hernia or knee?"
"You're both wrong, and I'm wrong" cried the hobbling man, "I thought it was a fart"