Some of these pictures and descriptions may give away plot details that you might not want to know before watching the film.
This is a horror movie about soul stealing, demons, mountain witches, and how if little girls don't say their prayers, the devil will carve a bloody cross on their back, make them cough out dirt, and suck their soul out of their mouth, leaving them dead with melted eyes... and other nonsense. Skip this one. The snake scene isn't even very interesting. Julianne Moore is a psychiatrist working with a patient who has multiple personalities. She is looking for the family home of a man in the mountains of western Pennsylvania. She stops next to a ramshackle house scrawled with witchcraft graffiti and a wooden cross hung with severed chicken feet, skulls, and dismembered baby dolls and asks a man sitting at a picnic table in front of a trailer home for directions. He doesn't respond, he just starts milking venom from a snake, then blows into the snake's mouth, so she leaves. That's it. The hanging chicken feet weren't creepy enough so the director had to throw in a snake. I think they want us to believe he's going to use the venom in some kind of witchcraft, but maybe the guy was just doing some volunteer work for the local anti-venom manufacturing facility. What's so creepy about that? The man also has a milk snake in a small glass terrarium. We don't get a good look at what kind of snake he's milking. We don't see a rattle, or much of the head, and the pattern is blurred, but from the large white patch above the mouth, it looks more like a Cottonmouth than a rattlesnake. Cottonmoouths don't occur in western Pennsylvania where the film is set and where it was filmed, but since when has that ever mattered in a movie?