Keira Knightley practised sex faces in the mirror for 'A Dangerous Method'.

The British actress plays the role of Sabina Spielrein - who finds sexual gratification in spanking - in the movie about the relationship between Carl Jung and Sigmund Freud and revealed she worked on getting her facial expressions right before showing them to director David Cronenberg on internet phone service Skype.

She told The Sun newspaper: "I asked psychoanalysts about it and they said, 'Sex and anything like that is trying to release energy, trying to release pent-up emotion'.

"So I worked with that and sat in my bathroom and pulled faces at myself for about two days, trying to figure out what it was going to be.

"Then I got on Skype with David and went, 'I've come up with this', or, 'I've come up with this', and he went, 'That one!'"

While the shoot was intense, especially filming two scenes Keira refers to as "masochistic", she was able to switch off after work by watching the soccer World Cup.

She said: "People talk about how infamous the post-job blues are and I think a lot of that has to do with re-finding where you are and getting the other thing off.

"You do find you're suddenly in a mood in the middle of playing something and you think, 'Is that my mood or is that actually nothing to do with me? Is it this other character that I've got living on my shoulder at the moment?'

"That was not the case with this at all. In fact, quite the reverse."

"At the end of the day we moved on and watched football -- the World Cup was on and we had a beer and a really nice time."