Near the end of the film - as Ronan's ship, The Dark Aster, crashes to the ground - Groot creates a protective cocoon for the rest of the team. It all gets very emotional and Groot says:
We are Groot!
As far as I was aware all he can say is "I am Groot". How is he able to do this?
I've seen this related question that covers his background and that he used to be able to speak quite a bit. This question is more about how "this" Groot can say "We are Groot" when he usually only ever says "I am Groot".