A doctor, Joe, and a lawyer, Mark, were talking at a party.
Their conversation was constantly interrupted by people describing their ailments and asking Joe for free medical advice.
After an hour of this, an exasperated Joe asked Mark, "What do you do to stop people from asking you for legal advice when you're out of the office?"
"I give it to them," replied Mark, "and then I send them a bill."
Joe was shocked, but agreed to give it a try.
The next day, still feeling slightly guilty, Joe prepared the bills.
When he went to place them in his mailbox, he found a bill from Mark, the lawyer.
