Dan married one of a pair of identical twin girls. Less than a year later, he was in court filing for a divorce.
"OK," the judge said, "Tell the court why you want a divorce." "Well, your honor," Dan started, "Every once in a while my sister in law would come over for a visit, and because she and my wife are so identical looking, every once in a while I'd end up making love to her by mistake."
"Surely there must be some difference between the two women," the judge said. "You'd better believe there is a difference, your honor. That's why I want the divorce," he replied.