For all the hype about Natalie Portman's steamy lesbian sex scene with Mila Kunis in 'Black Swan,' the scene was still tame enough to earn an R rating from the Motion Picture Association of America's ratings board, which means it can (and will) be shown in theaters all over the country. Like Portman, Michelle Williams is on the receiving end of an oral sex scene in 'Blue Valentine' (opening Dec. 31). Despite the similarity of the scenes, however, the Williams scene earned her film an NC-17 rating, which would keep it out of most mainstream theaters, out of the movie-section ads in many newspapers and off the shelves of most mainstream DVD retailers.

The directors of both films acknowledge a double standard at work here, according to the Los Angeles Times. The Times article, however, merely hints at what the reasons might be for such a double standard, saying only that the 'Blue Valentine' scene is more "emotionally authentic" than the 'Black Swan' scene -- which is to say, it's more convincing and realistic and less fantasy-like. That's certainly one possible reason, but there are others that go unmentioned in the article.