Contradiction
In the beginning when Zooey is calling her friends about getting engaged, her and her girlfriend talk about Peter and Zooey being in Mexico (I think) and it being "oral" and not sex. They talk about that trip not being the first time Peter and Zooey had sex because Zooey was on her period.
Later in the movie they talk about how Zooey does not go down on Peter.
So either they are contradicting themselves or they are referring to Peter getting his red wings. Which is it?
The end.