Joss Whedon writes beautiful drama. His sensitivity and his sense of drama and scenes are pretty exceptional. There's no one else writing like him, really, in sci-fi and TV. That's not to say there are no astonishing writers on TV. I was nervous about coming to America and playing an English person who speaks very English when all the writers are American, because it's a very particular thing to imitate, and if it's badly imitated, it sounds painfully contorted and silly. And he writes very well for English people. It was Joss Whedon who persuaded me.

I'm not much of a Method actress, so even though my character in The Ghost Writer was quite dark and bad-tempered, I could only do that if I was seeming quite perky.

Working with Roman Polanski is funny. It's like anything in life - someone warns you that something's going to be amazing or difficult or awful, and you say, "I can do that. I can cope with that." And then when you're in the middle of it, it may be joyful or tricky, but it's never difficult in the way you think it's going to be difficult.

There's this absurd situation on a movie set where your trailer's here and the set is here and the lunch tent is here, and you're not allowed to get yourself from these three places.

My analysis of the situation was that Roman Polanski wasn't trying to break us down or get a performance out of us by destroying us. He was absolutely, very simply, trying to recreate this clear picture in his head. And the pictures he creates are absolutely perfect, and they are exactly what he saw in his head.

We had an ancient Russian acting coach at my drama school who said the worst offense you could commit was to let your subtext show. That is the point of acting, is to be saying one thing and not be allowed by society or your predicament to show what you're really feeling. In a way, I think that's why the therapy generation has killed script writing, because all you ever get is people going, "Hi, I'm feeling really angry right now."

As I was getting into the helicopter, a slightly nervous actor said to me, "Whatever you do, don't say to the helicopter pilot, 'Show me what this baby can do.'" So I of course, got into it and said, "Show me what this baby can do." And we just had this insane helicopter ride. It's the sort of thing you only get to do on movie sets. I'm so lucky to have done it and have that chance.