If there is a more adventurous actor out there than Tilda Swinton, I am not sure who it could possibly be. The Oscar-winner (Michael Clayton) cannot be accused of taking obvious roles. In offbeat projects—from her beginnings with Derek Jarman to Orlando, Julia, We Need To Talk About Kevin, Moonrise Kingdom and so many others—Swinton has become a favorite of some of today’s top directors, including the Coen brothers and Wes Anderson. This year alone she’s already received an Independent Spirit Award nomination for Jim Jarmusch’s Only Lovers Left Alive, wide praise as Madame D in Anderson’s The Grand Budapest Hotel, and taken on such off-the-charts characters as Dr. Shrink-Rom in Terry Gilliam’s The Zero Theorem and being barely recognizable as the Margaret Thatcher-like matriarch in Bong Joon Ho’s thrilling Snowpiercer. That role was actually written for a man, but rather than having it rewritten, Swinton went into it with all her usual abandon and made it her—or is it his own?

I was surprised to hear this was actually written for a man originally, right?

It was written for a “mild-mannered man in a suit” and Bong Joon-ho and I were friends and we were trying to find something to work on together. I read (Snowpiercer) and I saw there was nothing for me, but I was really keen to see the film. Bong wrote to me a few weeks later and said, “What about the mild-mannered man in a suit? Who do you imagine?” It was like trying to make fire with two wet sticks. It kind of slowly dried out, slowly dried out, and I started to have a very wicked fantasy.

So how much re-writing and how were you involved in re-shaping the character at all?

No re-writing at all. As you can hear, Mason’s referred to constantly as “sir,” and “he,” and then sometimes people said “she.” You know what? What’s a gender between friends? I think it’s, so who knows what Mason is?

What was it that attracted you to the ideas in this film, the themes of it?

Of course, originally it was Bong, and I would do anything with Bong. I think he’s really a master. With each film he makes a universe that’s completely unique to itself. That’s such a dream, as a filmmaker, to work with filmmakers who do that, because you step through the looking glass into this whole world. I loved the idea of the revolution moving up the train, and when in the tail section getting to see a sushi bar or going through a hairdresser’s salon. It also feels so cinematic. It’s almost as if every carriage is a different homage to a different filmmaker. So you sort of go through your Fellini section, and you go through Delicatessen. It’s like going through cinema.

Did you have specific ideas about how you wanted this character to appear?

We started out with this gesture that we were going to do. I started to think about dictators. What’s the most sinister thing about dictators, actually, is the way in which—with a little bit of hindsight, or even at the time—we turn them into clowns. We end up finding them rather endearing and hilarious. So I was thinking of monstrous clowns and thinking that that might be a way of disrupting this mild-mannered man in a suit. It would be nice to throw a different shape. So between us, Bong and I started to think of clowns, and it so happens that the real grain at the heart of Mason is someone from my own life who I can’t name, for the sake of sensitivity, but someone in my childhood—someone who was kind of that shape, who was a bit dictatorial and had made that sort of noise, and didn’t actually look like that. Put it this way—when my brothers see this film, which they haven’t yet, they’re going to laugh a lot.

I always wanted to play a character with a nose like that because of what it does to the eyes, actually. So we got a piece of sellotape and put my nose up, and then we thought, “Oh, well, then maybe I’d better have some teeth.” So we wrote it down, “Let’s get some teeth.” What about some googly glasses? What about a wig that kind of moves around? And huge breasts? It was like Halloween, basically.

Logistically, how was this film shot?

We were in a train. We were in a real train in a big studio in Prague, and the train was a series of about ten carriages, and they moved on a gimbal. So all that movement, you know, we didn’t have to fake it, which is a great relief. So it was very interesting to be on a shoot where the first thing that would be shouted out before “Roll cameras” was “Gimbal.”

Yeah, it looked like very close quarters in some of it there.

It was fascinating to see Bong and our cinematographer working out how to shoot it, because if you’re going to be shooting an entire film in a carriage, you’ve got limited angles. They work in Korea, apparently, quite regularly, they work with the editor right there on the set, and they assemble a rough cut as they’re shooting. It’s like putting together a jigsaw, and I’ve never worked in that way before.

You play such interesting roles all the time. What do you look for?

I don’t look for roles. I’ve always gone for the conversation with the filmmaker because that’s how I started. I started working with one filmmaker, Derek Jarman, who I worked with for nine years over seven films, and that was the first principle. Then the second principle was, “What’s the film going to be?” And then the third principle was, “What might I do in it?” Sometimes there was nothing for me, and sometimes there wasn’t even a mild-mannered man in a suit. Going for the role is not something I’ve ever learned to do. I feel in terms of my own wiring it’s so important to be in league with my comrades; I wouldn’t want to just sit in my trailer, working out a role by myself. I really like to feel in a conversation with the filmmaker. So in answer to your question: whatever comes along. What comes along is conversation, so it’ll either be a conversation with someone I know, or it’ll be someone new, like Bong, who I didn’t know before, and we’ll just whip up some idea that’s interesting.

To hear Swinton talk about her transformation into Mason, check out the video below: