Dan married one of a pair of identical twins. Less than a year later he was in court filing for a divorce.
"Tell the court why you want a divorce," the judge said.
"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 identical, sometimes I'd end up making love to her by mistake."
"Surely there must be some difference between the two women," the judge said.
"Exactly, Your Honor. That's why I want the divorce!"