Black Snake Moan is a movie with an "interesting" plot: Childhood abuse has made a woman into "a nymphomaniac", always seeking sex with strangers. The cure is to chain her to a radiator wearing nothing but her panties. There she can moan and wriggle harmlessly.
Then add a layer of race onto this story of fairly obvious misogyny. Make the woman chained to the radiator white and the man who does the (well-intentioned!) chaining black and set the whole story in the American South. What do you get? A masterpiece which is something quite different than the sexual violence it sells, because it has reversed racism?
Lakshmi Chaudhry summarizes what is wrong with movies like this one:
The movie's misogyny is hardly surprising from a director known for promoting the dubious proposition, in Hustle & Flow, that "it's hard out here for a pimp." But what passed for mere indifference to women in that movie is revealed to be an unmistakable lack of compassion in Black Snake Moan. Rae is a victim of childhood abuse who channels her pain through a raging appetite for sex with strangers, which finally gets her beaten, raped and left for dead on the side of the road. In Brewer's world, however, it is Rae who needs to be "cured" and not the men who heedlessly use her for sex, with or without her consent. So along comes Lazarus to help her "collar that dawg," which is her libido.
But that would spoil the whole purpose of the movie which is to ogle at the almost-nekked woman chained to the radiator while pretending that it isn't sadism.