Black Swan and Blue Valentine have more in common than just colors in the titles. These movies also feature their gorgeous stars getting their muffs munched. But there's one big difference: Black Swan's Mila Kunis-on-Natalie Portman cunnilingus scene got an R-rating, while Ryan Gosling chowing down on Michelle Williams earned Blue Valentine an NC-17.

Why?

The L.A. Times recently explored what might be the reasoning behind the ratings, but most agree that it comes down to a question of believability--Valentine's moaning, groaning, orgasm-filled scene seems more "genuine" than the druggy, fantasy-like lez-out of Black Swan.

And the directors agree (via Popeater):

"The essence of our film is that it's intimate and emotional and the sex doesn't feel fake. It's an honest relationship between two people, and it feels real because I have great actors," 'Blue Valentine' director Derek Cianfrance told the Times. "It's as if the MPAA is saying, 'Your actors are good -- but they're too good.'"

'Black Swan' director Darren Aronofsky seems to agree. "I've heard the 'Blue Valentine' scene is more emotionally authentic," he told the Times, noting that he hadn't yet seen the film. But Aronofsky's problem with the ratings board is more that it seems to rate violence more leniently than sex, "which to me seems totally backward."

Frankly, at Mr. Skin.com, we don't care what rating a box-chewing scene gets as long as there's nudity. So for the best in lap-licking with plenty of skin, press play on our brand-new playlist: Best Cunnilingus Scenes (Part 1). Go on. Have a taste.

UPDATE (12/8/10): After an appeal from The Weinstein Company, the MPAA has revoked Blue Valentine's NC-17 rating and given in a straight R... without even cutting out the cha-cha chewing scene! Sometimes the nude guys win.