In the footage we saw today, there's a scene of Snape and McGonagall facing off in the Great Hall, which I don't remember happening at all in the book.
They do face off, but it's not in the Great Hall. There are a lot of things there that are slightly different from the book, but they are true to the spirit to the book. Snape and McGonagall do face off in the book, but it's in a corridor as Harry's on his way to the Ravenclaw common room. It didn't work the way we were structuring the final battle to have that, so it takes place in the Great Hall. We also wanted to make a bigger scene of Harry's confrontation with Snape. Snape's role in the film is minimal, and it was minimal in the second half of the book, and yet you wanted to have the emotional investment when you see his past story [the memory Harry views in the Pensieve]. We wanted to build that up in order for it to have its emotional impact.

So the Pensieve moment stays in too?
Yes, that and Dumbledore [at King's Cross]. But what I love about these films, what I love about the books, is that all the action, adventure and magic, what means most to me is the character stuff, the slow stuff. I love having the time to tell the story. I'm really happy about breaking the book into two films, it gives us the time to really spend time with the characters and have the moments such as the flashback, Dumbledore at King's Cross. If we had done it as one film, we would have lost the Snape flashback.

Is the mewling creature on the floor at King's Cross still in there?
Yes, that's in there.

I've never been able to figure out what that means.
It's part of Voldemort's soul.

There's the scene from the first half of the film of Hermione and Harry dancing in the tent, and it's so rare to see any scenes added in the Harry Potter movies, but people loved it. Is there anything like that coming in the second half?
I'm not sure there are. For example, like you saw in the footage today, the statues coming to life [during the Battle of Hogwarts] -- that's not in the book. It's quite a percussive ending, and we wanted to have some good magic.

Do you keep the desks that Professor McGonagall is instructing to charge?
No, we didn't.

Oh, I loved the desks!
I liked the desks too, but if you think about it, in a film which has grown up, that's kind of juvenile. It's like Peter Pettigrew strangling himself [which happened in the seventh book but was cut from the film]. It's great in the book, but really hard on film. Those things don't translate as well when the films are growing up.

When you went back and reshot the epilogue at the end of the film, was it mostly tweaking the makeup effects?
It was a couple of reasons. One it was the makeup, that was the first thing. The other was, to be honest, we were limited by shooting at King's Cross. It really limited our ability to block. And in terms of performance, these little kids, some of who weren't actors, were drowned by the noise of the trains, the announcements. That was really a problem. When we filmed it back at the studio, we brought the trains to the studio and filled the station in digitally. It's really beautiful.

Are most of the effects makeup, or is there any CGI in there?
Not really. A little bit of tweaking.

How did the actors go into the scene, growing into themselves 15 years later?
They look good. It's subtle. It's going to be very interesting to see the response, since inevitably we know it's Dan, Rupert and Emma, and we've just seen them as 17-year-olds. Initially we went a little further [with the effects], and then we pulled it back. Sometimes if you try too hard you're really aware of the work. You won't have huge wrinkles, obviously there's a difference, but you still resemble yourself.

You had this opportunity of releasing the first half of the movie while the second one was still underway. Did you take anything from the response to the movie and apply it to the second half?
No, we've never done that with any of the films. I am a really big Harry Potter fan, and so too are the directors and everybody working on the films. In a way we are the harshest critics of the films. I'm aware of everything that's wrong with each and every one of the films, proud as I am of each. There's nothing we can be told-- we're the critics, we really have a good sense of what we ned to do.