Usually the books should give you hints if you have read all 5 of them so far, but yeah the movies turned out to be a bit different when you actually see them. For example, In the 3rd book (POA), Ron has to face a spider (Or the Boggart), and he makes his legs fall off, but in the movie he actually makes the spider wear skates and fall over. Do you get my drift? Hopefully you do..;;