Your movie Hunger starred Michael Fassbender as Irish republican hunger striker Bobby Sands. Why go from that to this?
I mean, it’s like any other director. You sort of go from one subject to another subject. It’s not so radical, really. It’s just one of those things where this is what interested me at the time. The process started with myself and [co-screenwriter] Abi Morgan having a conversation and talking about the Internet, and from that, pornography, and from that, sex addition. And that was sort of a seed that was planted. And then we went to research the project in New York City with experts in the field and were talking to people on the ground, people who actually have this affliction, several people. Just in-depth interviews because there was no story, there was no narrative, just an interest. I mean, it could have turned into a dead end, but the research led us to this point.

Did you know people who were sex addicted?
No, I didn’t know anyone. I suppose everyone has seen it. I’m not a sex addict, if you’re asking me that question. Nothing personal.

What did you find out from the experts about sex addiction?
It’s similar to alcohol addiction, similar to most addictions. There’s nothing sort of unfamiliar about it. Of course, when I was told about the idea of sex addiction, I laughed, like most people do. But then you realize it’s similar to a person who’s an alcoholic, when that person cannot survive through the day without drinking one or two bottles of vodka. Similar to sex addicts: They cannot survive a day without having some kind of sexcapade. Then it ceases to become funny.

And that’s where shame comes in.
The idea of shame, the word, shame, came about through talking to a lot of these people who have this affliction. They went on these sexcapades, as such, and when they came out the other end of it, there was this feeling of, really, self-loathing, of feeling shame that came over them. It kept on coming up as a word. It kept on coming up again and again and again. I thought, Well, this should be the title. And in order to sort of get over the shame, of course, what they would do is start over again with the sex, similar to any addiction.

Where did the idea come to introduce a sister [Carey Mulligan] who also is very troubled?
I wanted to also make it a kind of love story in a way of siblings. One of the characters is exploding and the other character is imploding. Carey being exploding, and her brother imploding. But they come from the same background. They come from a place … as she says in the movie, “We come from a bad place. We’re not bad people.” And how they deal with it.

But you don’t say what happened to them.
You know, I didn’t want it to be mysterious. I wanted it to be familiar. And in order to do that, I thought, you know, everybody will have some understanding of what that might be. You bring people in to see a movie, but you ask them to bring in their intelligence and their knowledge as well, so what happens in that situation is they understand it far more than if there were details and it was specific and blah blah blah. They can bring themselves and their own histories and their own experiences to the movie. But also, you know, sometimes in a movie you don’t need a head and a tail. You just need a tosser.

Did you include Carey singing “New York, New York” very melancholically as a way to highlight New York being the ultimate place for sex addiction?
I didn’t say it was the ultimate place. I never said that. It could be in L.A. or New York, but it’s New York because it’s a place where people want to talk and it’s a place of access and excess and it’s an interesting place for a character like Brandon. But it could be any place in the world. The whole idea of “New York, New York” is, if you read lyrics, it’s a sad song. “New York, New York” is a blues. Bessie Smith should have sung that song. I know Liza Minnelli and Frank Sinatra sing it in a very triumphant fashion, but if you listen to the lyrics, it’s very sad. I mean, it’s a person who’s obviously poor — “these vagabond shoes” — possibly a vagrant to some extent, who wants to make it. It’s a dream that is not fulfilled at all. It’s a dream. So I thought of actually putting it on its head and working to make them play the song right. And what it does is it talks more about their relationship, Brandon and Sissy’s relationship. It’s the only time when Sissy has a situation when she’s talking to Brandon, or having a communication with Brandon, which is heard and responded to. It’s the only time he actually listens to her in the whole movie, and it happens in a very abstract form as within this song.

The premiere in Toronto was actually on September 11, and that was quite poignant when Carey sang that song. A number of people, I heard, were crying in the audience. It was a very cathartic moment for a lot of people. Because when she’s singing, she’s singing not just about their background and where they came from, but the environment that they’re in. It was very moving

At a press conference, Fassbender said he imagined that his character Brandon had once played piano and gave it up and was missing music in that moment.
Nah, I think that’s Michael going off on one.

How did you shoot Fassbender differently in this movie than in Hunger? He’s starving and unsexy in that movie, and robust and virile in this one.
I don’t know. I think it’s eye of the beholder. I was interested in ritual. You know, someone gets up in the morning, they have a glass of water, they go to the bathroom, they have a shower. So by just following the ritual, it’s kind of beautiful.

Why did you decide within the ritual to include full-frontal male and female nudity?
People get up in the morning and they go to toilet and they have a thing of water. They don’t even think about that. It’s not about me including it. It’s quite normal. It’s the most unexotic thing in the world.

How did you make the nudity comfortable on the set?
Just do it. I mean, it’s of no big importance. Half the people that are going to see this film, hopefully, have exactly what that person is walking around with. It’s of no shock to them at all. And 99 percent of the people will have seen it before. It’s of no interest. I mean, I’ve never seen anybody shot in the head with a gun before, so I think that would be, to me, much more startling than that. It’s of no big … it’s not titillating. It’s not exoticized. It’s just a guy having a piss and a glass of water and going to have a shower.

There’s also lots and lots of sex, and long sexual sequences.
Well, there’s one scene where he’s trying to make love, with Nicole Beharie’s character, Marianne, which is very sensual. It’s for me, very sexy. But we have to see it in a long shot because we have to see that he’s attempting to sort of make an emotional connection. Okay? He’s attempting to make an emotional connection, but it fails. It breaks. It fails. So we have to go through that in order to see him sort of trying to connect. And of course when we cut to him having sex against the window with this woman, it’s very quick. It’s very matter of fact. Do you want a drink? No. Do you want me to help you with your bra? No. And it’s out. So we know what that’s about. But the emotion, what helps from this long shot is the emotion of him trying, is the effort. He really wants to, but he can’t. For example, with the threesome, it’s actually a foursome, because I’m bringing the viewer in. It’s in a way, it’s not at all … it’s about his ecstasy within it, but it’s the saddest ecstasy in the world. For me, at least, it’s the saddest ecstasy in the world, because he’s trying to get something out of it. But ultimately, it’s quite tragic.

What’s changed about Fassbender as an actor since Hunger?
Nothing. I mean, this is not just a Michael Fassbender movie. It’s a Carey Mulligan movie. Carey Mulligan is spectacular in this movie. That’s something we have to get across. And Nicole Beharie, a newcomer. Nobody knew about her before, really. People are talking about her now. She could be a star. James Badge Dale. My god, James! It’s an ensemble piece. It’s not just a Michael Fassbender movie.

I just asked that because you worked with him on your last movie.
Not much [has changed], really. It’s all about risk-taking. He’s an artist. He’s not an actor. There are a lot of actors out there, but he’s actually an artist. There are a few artists — not a lot.

What did you discover about New York while shooting this?
Well, we shot in winter. It was really snowing at that time. So I realized, “Don’t go in winter.” But what I liked about New York was the people. I’m not kissing anyone’s ass, but honestly to God, crews in New York work so hard and they’re treated very badly. We were very much taken into their heart and they’re fantastic. Also my son came over, so Central Park, the children’s play area, was wonderful. And the subway is great. Who needs taxis? New York, you know, it has a big heart.

You shot a lot in the Standard Hotel. Do you get free rooms there now?
God no!