What's Shakin'

5 couples go out to eat. Some people know each other and others don't. So, every one who doesn't know someone will shake hands. Obviously a wife won't shake their husband's hand. At the end of the meal, one of the husbands, John, is curious and asks, "How many hands did everyone shake?" He got the following answers from the other nine people. 8, 7, 6, 5, 4, 3, 2, 1 and 0. How many hands did John's wife shake?