Playing a character with multiple personalities is a dream job for an actor who likes to immerse himself in his roles. So James McAvoy didn't hesitate to sign up for M. Night Shyamalan's new blackly comical horror thriller Split. Although he admits that the script's opening pages, in which his character Kevin kidnaps and mentally taunts three teen girls, made him pause.

James at the US premiere of SplitJames at the US premiere of Split

"That worried me," McAvoy says, "but then as soon as Kevin came in the room as Patricia, I was like, 'Ah, right! I'm gonna have fun with this.' It's not just sensational, but something that could be hopefully intriguing and compelling in a way that isn't just edge-of-your-seat nerves. And as an actor there was also the opportunity to flex many muscles and employ all the dexterity you can muster."

This meant that he had to prepare to play nine roles instead of one. "I got the role quite late in the day, so I had to do nine times the amount of preparation in really less than half the time that I would usually get to prepare one character," he laughs. "The other thing that was interesting is that, apart from Kevin, all the other personalities that lived within the same body, they had a different kind of genesis than you or I. You know, you or I are born because our parents did the do, but they're born out of a necessity to perform a pretty specific function within the larger group. That's because they each personify a certain quality or qualities that Kevin has."

More: James McAvoy broke his hand filming Split

And McAvoy readily admits that one of the identities was harder to play than the others. "Patricia," he sighs. "Simply because she wore high heels that I was told repeatedly by the women on set were very comfortable high heels. But they gave me nothing but grief."

As an actor, McAvoy relishes taking on smaller, offbeat roles like Kevin in between the blockbusters. "Even though I'm established," he says, "even though I've got X-Men behind me and it's helped me buy my house, I always feels like I need to take a challenge. So what's the harm in throwing yourself in there? It's just your reputation! I don't care if people get a bit shocked by something edgy. There's just so much pacification in cinema, and I've been involved in it at times. I've done films that make people fall asleep. So I'm quite keen to push the envelope."

Watch the trailer for Split: