A doctor answers his phone and hears the familiar voice of a colleague 
on 
the other end of the line.
"We need a fourth for poker," said the friend.
"I'll be right over," whispered the doctor.
As he was putting on his coat, his wife asked, "Is it serious?"
"Oh yes, quite serious," said the doctor gravely. "In fact, there are 
three 
doctors there already!"