Not to sound too much like Jerry Seinfeld, but what is the deal with Black Swan actresses and their use of body doubles?

First we had Natalie Portman’s did-she-or-didn’t-she dance controversy. And now Swan co-star is claiming she used a body double -- or, more appropriately, a butt double -- for her raunchy sex comedy Friends With Benefits, which opens everywhere today.

While promoting the film on Ryan Seacrest’s radio program, Kunis admits that she does show “side boob” (Josh notes: Having seen the movie... I can say it's a little more than side boob) in director Will Gluck’s comedy (which is wall-to-wall sex scenes between the brunette beauty and Justin Timberlake), yet she held off on baring her derrier because she “can't just give away everything all at once. ... I gotta let it all out in little pieces here and there."

Also, in what is one of those strange things that only happen in Hollywood moments, Kunis tells the American Idol hosts that she sat in with Gluck and the film’s make-up artist as they auditioned female asses to play Kunis’s stand-in. "These lovely women had to show us their derrieres, and the chosen one resembled my body the most without looking like it's fake," she tells Seacrest.

It doesn’t look fake in the scene in question, which shows Kunis walking down the hall with her rear in view. And since, at that point, you’ve already seen the Black Swan starlet mostly topless, you kind of assume that the butt belongs to her. The really weird thing here, and the real reason we're bothering to report this, is that faking it sort of goes against the mission statement of the movie, which proudly declares its intention of flying in the face of clichéd romantic comedies that have come before it… the film fights throughout its running time to be one of those edgy, raw, we're going to approach sex and nudity in a real way on screen movies. Only it isn't, and in the end it embraces most of the same clichés before the end credits roll. Apparently that includes finding a butt double for your gorgeous, up-and-coming leading lady.