Some of these pictures and descriptions may give away plot details that you might not want to know before watching the film.
I had to watch this movie just because of the title. I had no choice. It's a made-for-Netflix horror movie starring Carmen Ejogo. She's Katrina, a single mother driving from Phoenix to Oklahoma with her 5-year-old daughter Clara. Somewhere in Texas she pulls off the main highway to avoid traffic and takes a smaller road. She gets a flat tire and while she fixes it Clara wanders into an open field where she walks next to a rattlesnake and it bites her. We see bite marks on her leg. Katrina carries her to a trailer nearby and tells a woman that her daughter was bitten by a snake. The woman tells her to leave the child and let her help her, that she has worked on many bites. As Katrina leaves, the woman ominously says "We'll discuss payment later." This "payment" is what the rest of the movie is about. When Katrina returns to get Clara, the woman is gone, and Clara has no bite marks on her leg. She takes Clara to a hospital in the nearby town of Tulia, but the doctor sees no rattlesnake bites and thinks it's Katrina who needs help. He keeps Clara overnight thinking she has sunstroke. Then s**t gets crazy. Katrina learns from a man with a bloody shirt who appears in the hospital room that she made a deal with the devil, and that she has until sundown to kill anyone she chooses or Clara's bite will return and she will die.
Katrina returns to the place where Clara was bitten. A tanker truck stops and a man walks up to her with a tire iron to threaten her. He looks like some kind of walking dead zombie with several large bloody bullet holes in his body. She sees another rattlesnake and throws a rock at it. The man disappears and the snake crawls away. She googles murders in Tulia and discovers several examples murders, including the truck driver, the man in the hospital and other people she has talked to. The rest of the movie deals with Katrina's decision whether to kill someone to save her daughter, and who to kill.
Katrina finally finds someone worth killing - a violent man who beats up his wife. She buys a gun, but can't bring herself to shoot him in his home so she kidnaps him and takes him out to a deserted canyon, but he knocks her down and she loses the gun. Then, suddenly, a rattlesnake appears and bites him, and he falls into an arroyo. We see snake bites on his leg. Obviously, the rattlesnakes are working with the devil in some way. That's not a stretch given the reputation of snakes in fiction (and the Bible.) That's enough spoiling. Watch it to find out the rest.
The rattlesnakes we see are all live snakes, except that during the two snake-bite scenes it looks like they added some digital effects to portray the biting head. The credits list three snake wranglers (for the live snakes) but they also list a Snake Puppeteer, which indicates that there was some manipulation of fake snake props or maybe live or dead snakes. The snakes appear to be Western Diamond-backed Rattlesnakes, which should be found in the Tulia area of the Texas panhandle, but one of them might be a Mojave Rattlesnake which occurs far from that area. It's hard to say. However, though we don't know exactly where they are going in Oklahoma, I doubt they could have ended up in Tulia, which is too farm from the main highway they should have been driving.