I think it's very interesting for a director that enjoys thrillers and mysteries like I do to have the challenge to do that.

Obviously in the close-ups we bring extras around or we do it later, but them running in and the big shots, they don't know. They're just coming out.

I could only shoot when the subway was on the other platform. Little things like that, and the platform is very narrow. It's not like you can hide if a subway comes so a lot of things happened because of that. Or a thousand people just came and looked straight into the lens like they didn't expect a movie to be shooting.

The hard part on the subway is that you have, let's say, eight hours, but you have to hit these deadlines. From here to here, you can use this part. From this time to this time, you can use that part, and you have to hit them and it gets very stressful.

I think video is very useful, but it's very useful when you want a certain reality.

You have to think of each stage of the movie and how it progresses, get into the state of mind of the character, and then match the camera to that, and keep making it tighter and tighter and crazier and crazier so people don't get bored. You know you cannot do a similar shot that you did at the beginning of the movie at the end.

These days in movies you can always come back to a location or do an insert or do something, so that's not even an issue any more. But coming back every day to the same plane, it messes with your head.