In director David Cronenberg's new film about Carl Jung, Sigmund Freud and the birth of psychoanalysis, "A Dangerous Method", Keira Knightley plays Jung's formerly hysterical patient and lover Sabina Spielrein.

The movie debuts in U.S. theaters on Wednesday, and Knightley told Reuters back in September at the Toronto film festival that she initially turned down the role due to its spanking sex scenes opposite actor Michael Fassbender, who portrays Jung.

But the 26-year-old British actress said the promise of such a dream role and working with Cronenberg, Fassbender and Viggo Mortensen (who portrays Freud) was too enticing to walk away. It also helped that Cronenberg promised the spanking scenes would be clinical, not "sexy."

Q. Before the movie, what did you know of psychoanalysis?

A. "Absolutely nothing. I mean I had obviously heard of Freud and Jung, and I knew vaguely that it was all meant to be based on sexuality and that your parents came into it somewhere. But apart from that, I really didn't know anything. So it was a question of starting from scratch."

Q. You've said you read "a stack of books."

A: "A Jung biography. And then 'Memories, Dreams, Reflections' and the letters between Freud and Jung. It was Nietzsche, a little bit of papers by Freud, papers by Jung and then I found a book called 'Sabina Spielrein: A Forgotten Pioneer of Psychoanalysis.' That was Jung's notes on Sabina and then her dissertations and several papers, essays about her and then diary entries. So it was quite a stack."

Q. Did you ever think about studying psychology?

A. "No ... there are a lot of parallels in acting. You are trying to understand the world from a different point of view without judging it. Looking at it from a psychological point of view is something you do naturally as an actor anyway."

Q. Your depiction of hysteria in the film has drawn mixed criticism. How did you come up with say, your jaw movement?

A. "That's the tricky thing, when you are reading a script that says, 'has a hysterical fit, ravished by tics'. And you go, 'OK, what does that mean? And what do you mean a tic?' So really, a lot of the reading was based on trying to get descriptions of tics and trying to understand what that was.

"I wanted it to be shocking, because what was going on internally (for Sabina) was shocking. I just thought, I wanted to reflect that externally as much as possible, so I literally sat in my bathroom pulling faces at myself until I came up with this jaw thing. And I thought, 'Well that looks vaguely demonic,' and then I got on Skype with David (Cronenberg) and I had about two or three ideas and he went, 'That one.'

Q. Is this your most difficult character yet?

A. "As far as a role, every actor wants a role like this. It sounds perverse to say it's fun, but it's so interesting. Trying to understand that, to get into that point of view. Particularly if it's a filmmaker like David Cronenberg. I would have had serious reservations playing an hysteric with a director whose work I didn't admire as much has him."

Q. Every actor says sex scenes can be difficult. These seemed particularly so. Would you agree?

A. "They are always difficult and they are always exposed. This one was, sort of, something quite different...There were these two scenes, and I didn't know that I could do those two scenes. In the age of Internet and all the rest of it, I didn't know that that is what I want particularly to be out there.

"I phoned him up initially to turn it down because I thought they were incredibly important for the piece. So it wasn't a question of trying to negotiate them out of the film because I thought they were very necessary for the film. But I just thought, 'I don't think I can do that.'

"So, I phoned up David and said, 'I love you, I love your work, but I really don't think that I want to do this.' And he said, 'Well it would be a tragedy if you turned the role down because of that, so if necessary we can take them out.' And I said, 'No, because I understand why they are there'. He said, 'Well look, I don't want it to be sexy, and I don't want it to be voyeuristic. I want it to be clinical.'

"We talked for quite a long time about exactly what it was and trying to understand it psychologically. Once we discussed, I said 'Alright, fine, as long as it is not sexy. That brutal horrible aspect is kept, and it isn't a sexy spanking scene.'"

Q. Do you ever look back to learn from any performances?

A. "I don't watch any of them. I haven't seen 'Bend It Like Beckham' in nine years. It's all a learning curve. There are going to be good performances and there are going to be bad performances. There are going to be experiences where you click with people and experiences where you don't. There are performances that I know just from having been there where I haven't done well, just because I couldn't, for one reason or another. And then there are performances that I know on the day, actually that was pretty good."