Robin: Barney and I tried and failed. That was two years ago. Why would I ever go down that road again? It wouldn't even make sense.
Lily: It doesn't have to make sense. It's chemistry. Look, I've always had a sixth sense about these things. And now that I'm pregnant... with this idea in my mind-uterus, I see things even clearer. You and Barney have the kind of chemistry that just doesn't go away.