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 weird designer-drug/time-travel movie in which we see a woman in the city go back in time to an undeveloped swamp where she gets bitten by a rattlesnake. It's definitely one of the craziest snake bite scenes in a movie, but if you buy the premise, it makes sense. We follow two paramedics as they are called to scenes with injured or dead people who it turns out had all taken a designer drug called Synchronic that causes users to go back in time for 7 minutes.
Four minutes into the movie we see a woman and a man in a hotel room each take the drug. (We have no idea what's going on at this point, but later we learn that taking the drug takes the user back to a certain time at the same location where they take the drug but for only seven minutes. Then they return to the time and place where they started.) The movie takes place in New Orleans, so we see people travel back to a time when the city was all swamp inhabited by alligators, Spanish soldiers, and indigenous people. The woman who took the drug watches swamp vegetation and a native man start to appear out of a wall in her hotel room. Then we see her partly in the present and partly in a swamp, lying on her hotel bed with a snake crawling between her legs and an indigenous man nearby. We hear a rattling sound and we see a rattle shaking at the end of the snake's tail. Later we realize that she traveled back to a time when there were Eastern Diamond-backed Rattlesnakes in New Orleans. This is confirmed later in the movie when the paramedics are called to the hotel.
When the paramedics find the woman they see a large snakebite wound on her leg. They are baffled that a snake could be in a hotel room, so they wonder if she is part of a Pentecostal snake-handling religion that uses venomous copperheads because they were called to such a scene before. They ask her what kind of snake bit her, but she is in shock and does not respond. A man who appears to be a security guard or maybe an animal control officer tells them the bite marks and the woman's reaction to the venom don't indicate that a copperhead bit her. He thinks she must have been bitten by an Eastern Diamond-backed Rattlesnake. However, he says, that species of snake has not been found in the state in decades. This makes sense after we learn about the drug's time-travel effects. Later we see someone go back in time to a similar swamp where he is chased by an alligator and a Spanish soldier.
The snake we see is not really a rattlesnake. It's a non-venomous constrictor with some kind of rattle device or a digital rattle added to it along with rattling sound effects. For safety reasons they couldn't use a real rattlesnake in the scene, but this may be the only time I'm going to complain that they did not use a fake rattlesnake in the movie because the first time I watched the scene I saw the harmless snake but missed the rattle and the rattling sounds which happened very quickly and quietly. So later I was baffled when I saw the snake bite. (I take things too literally...) I had to watch the first scene again to understand that the harmless snake was supposed to be a venomous rattlesnake. I doubt most of the audience had the same problem since it seems to be understood that all snakes in movies are killers.