What gave Carey Mulligan the jitters

“It was more nerve-wracking than the nudity.�

Thus speaks Carey Mulligan about what she calls her toughest scene in “Shame,� playing Sissy, the emotionally extroverted sister of repressed Manhattan sex addict Brandon Sullivan (Michael Fassbender).

Mulligan first appears in Steve McQueen’s psychological drama completely starkers, having barged unannounced into her sibling’s apartment, where Brandon encounters her taking a shower.

“It’s funny because I’ve never been comfortable with the idea of nudity before and have never done it,� Mulligan says. “And it just felt absolutely her [Sissy]. She is a character who wants to be seen. She craves attention to the point of sort of illness.�

But Mulligan says it was the moment when Sissy, an earnestly aspiring chanteuse, has to sing “Theme From New York, New York� to a packed nightclub that truly tested her mettle.

“Singing is incredibly exposing,� says the 26-year-old native Londoner, who’s currently at work on Baz Luhrmann’s forthcoming adaptation of “The Great Gatsby.�

“I sang a lot at school, I sang in my church choir, I sang in musicals at school. I wanted to be a musical theater actress until I was, like, 16. I’d love to do a musical. I’d love to do ‘Cabaret.’�

But singing the John Kander and Fred Ebb standard in “Shame� was no church picnic. The arrangement takes the familiar Frank Sinatra optimism and ebullience and turns it into an almost tragic and desperate plea, all in a drawn-out, five-minute version that leaves the camera in close-up on Mulligan’s face for nearly the entire duration. Then there was McQueen’s insistence on shooting Mulligan’s voice live, without dubbing, in one single full take.

“It was scary,� Mulligan says. “There couldn’t be any mistakes. So we did 15, 16 takes. And it was great. It was so much fun. After the first two takes, when I finally relaxed and started doing it, I loved it. Steve has an amazing ability to make you think you can do something that you know absolutely you can’t.�

McQueen says the scene was pivotal because it intimates the depth of the siblings’ connection and their shared, somewhat desperate desire to rise above unspecified traumas and reinvent (or lose) themselves in the big city. It’s the film’s only moment when Brandon, forced to listen to his sister, briefly lets us see deep inside him, McQueen says.