So over the weekend, there’s been a series of duelling interviews/press releases/etc over Natalie Portman’s performance in Black Swan, and how much of her character’s dancing was her versus how much was performed by Sarah Lane, her dance double. A Jezebel article points out that the timing of the whole thing is a little weird and pointless—Portman’s already won the Golden Globe and Oscar, and the movie is a success. Lane’s revelation, whether it’s believed or not, isn’t going to make that much of a difference to the movie’s bottom line. So…why does it matter?

The obvious explanation is that if Portman wasn’t doing most of her own dancing, the performance somehow suffers—it wasn’t a full portrayal of a ballerina having a mental breakdown. And I guess there’s an argument to be made there; the climactic moments of the film happen onstage, and if we know it’s Portman’s face superimposed on Lane’s body, maybe that would lessen the impact for some people.

The thing is, though, that climactic moment also involves Portman sprouting wings. That scene is not about the reality of her dancing; it’s about seeing what her character feels—and given that we’re already well, well into CGI territory, I’m not sure why having someone else do the footwork matters. Also, and I say this as a girl who took about ten years of dance lessons, ballet is really fucking difficult. Mind-blowingly so. It’s not just being able to spin or kick really high, it’s about performing feats of balance even for moves that look totally basic, and having a certain stance that we as audience members take for granted but is actually the result of years of practice, and about just generally being aware of your own body and its movements in a way lay people (and I’m including myself in this number—I took lessons as a decided amateur) don’t understand. Even if Portman just learned to hold herself like a dancer and move well enough to allow a professional dancer to be superimposed in, I’d consider that an impressive achievement.

So why the insistence (complete with percentage breakdowns! I’m expecting a pie chart press release any minute now) on Portman having transformed herself in eighteen months into something dancers work their entire lives towards? I can’t help but wonder whether it’s because such an overwhelming amount of the discussion of her performance has been about her physical transformation: how skinny she was, how she lived on coffee and worked out eight hours a day, just look at her tiny dancer’s body! If we agree she looked that way because she turned herself into a ballet dancer, then it’s a triumph of immersive acting. If it turns out she did all that just to be able to look like a dancer, though, then we’ve all been lauding an actress for being really really good at dieting.

Don’t get me wrong: I think Portman is a fantastic actress, and I think her performance in Black Swan is about much, much more than what she looked like. But I think a lot of the critical discussion of her performance has devolved into talking about her looks, and if we take the artistic merit of her dancing out of it, that discussion starts to look a whole lot like rewarding an actress purely for hitting extreme physical ideals. I’d argue certain people aren’t insisting on Portman’s dancing for Portman’s sake; they’re arguing their point because of what it says about themselves.