Miles Teller originally auditioned for the role of Four, but was told that he wasn't going to be getting the role. Months later, the producers watched The Spectacular Now (2013), and were so impressed that they called Teller and offered him the role of Eric, who is supposed to be at odds and intimidating towards the character Four. Teller turned it down because he felt that he wouldn't be able to pull off being intimidating towards Theo James. He was then offered the role of Peter, which he accepted after his friend and former co-star Shailene Woodley sent him a text asking him to accept the role so they could work together again.
Tris has turned the gun on herself, and Tobias' finger is on the trigger... she says, "it's me, look at me, look at me." He recognizes her and says, "Trin."
When Four throws the first knife, he has three more knives in his left hand. When he is about to throw the second one, the knives in his other hand disappear.