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 western ghost story written and directed by playwright and actor Sam Shepard that seems to be known mostly because it was the last film to be released that River Phoenix acted in before he died.
As two men are riding horses across the plains we see a rattlesnake coiled on the ground and we hear it rattling for a few seconds. This seems to be to remind us that this is a dangerous place.
Later, a young Native American woman riding a horse hears rattling and turns around to see a sidewinder. A few minutes later we see her roasting the snake attached to a long stick over a fire and then eating it. I assume it's the snake she's eating. We didn't see her kill it, but it was surely supposed to be the sidewinder.
We see a live sidewinder in the movie, but the action takes place in Llano Estacado, which is in Texas and New Mexico, where there are no sidewinders.