[What usually happens is people who think they'd make good cohabitors compromise on how they want to look after. If you always hated your nose you use the other person's nose, that sort of thing. It happens pretty often that people want to move into bodies of the other sex, too, like Book, and then they have to find a cohabitor who's shaped how they want. You can do this other times too, though, if you and somebody just want each other's eye colors or whatever,] says Holly.