The twins worried about virginity individually, and they worried about it together. But the most basic problem was one they never talked about: sex was something they couldn't do together. Someone would have to go first, and then the other would be left behind. And they would each have to pick different guys, and these guys, these potential boyfriends, would want to spend time alone with one or the other; they would want to be the most important person in Julia or Valentina's life. Each boyfriend would be a crowbar, and soon there would be a gap; there would be hours in the day when Julia wouldn't even know where Valentina was, or what she was doing, and Valentina would turn to tell Julia something and instead there would only be the boyfriend, waiting to hear what she was about to say, although only Julia would have understood it.

It was a delicate thing, their private world. It required absolute fidelity, and so they remained virgins, and waited.

- Her Fearful Symmetry, Audrey Niffenegger