I approach every part I'm asked to do and decide to do from exactly the same angle: who is this person, what does he want, how does he attempt to get it, and what happens to him when he doesn't get it, or if he does?
I never talk about 'Harry Potter' because I think that would rob children of something that's private to them. I think too many things get explained, so I hate talking about it.
I was coming from a very cerebral, dark, difficult, layered play by Christopher Hampton and doing an action movie in Hollywood (Die Hard) with explosions, and I was holding a gun.
I've learned, having been on a lot of sets, the good news is that by definition you are surrounded by experts. They get fired if they're not - unlike in the theatre!