The Doctor and Lawyer

a doctor  and a lawyer were talking over a cup in a pupular restaurant. Then conversation was constantly interrupted by friends who kept asking for free medical services.

"How do you stop people from asking you for advice when you are not in  your office?" the doctor asked.

"I give it to them - then i send them in bill later", the lawyer replied.

The next day, the doctor decided to send bills to those people who had sought medical advice from him.
When doctor checked his own mailbox he found bill from the lawyer. these means the secret was found.

Location: KIBERA, Nairobi, Kenya