Dan married one of a pair  of identical twins. Less then 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."