Sirius, james and Remus.?

Question:

Sirius, james and Remus.?

Ok, in the 3rd Harry Potter book they explain WHY Sirius, James and Peter can turn into animals...and why they wanted to. So, Remus wouldn't be alone on the full moon nights. Yeah yeah yeah. I understand that. I've read that book atleast 5 times.
BUT in the movie its different...In the Prisoner of Azkaban movie when Sirius goes after (werewolf)Remus, Remus attacks Sirius(in dog form)
how come he attacked him then and not before when they went to school together?
Is that a mess up or are they trying to say only James as a Stag and Sirius as a Dog could control Werewolf Remus, but they couldnt do it alone...huh?

Best Answer - Chosen by Asker: I've gotta agree with Geckoboy on this one. I think it actually did say in the book that Remus attacked Sirius, so it wasn't really a movie error. Keep in mind that as a werewolf, Remus has absolutely no control over what he does, he can't control anything because the werewolf state of mind clouds his judgement. After so many years of taking the wolfsbane potion, he was probably a little unprepared for something like that, not to mention that he probably hadn't transformed around anyone so he wasn't used to it.

A werewolf targets human blood as well, all those times with James, Peter and Sirius, they were always by themselves...I assume if there had been any humans round during Remus' transformations in the school days, James and Sirius would probably have to fight Remus too.