Some of these pictures and descriptions may give away plot details that you might not want to know before watching the film.
This is one of the best Spaghetti Westerns, with a classic Ennio Morricone soundtrack. Most Spaghetti Westerns don't use snakes since they're made in Spain and Italy where there are no rattlesnakes they can easily use. This one features one of the most creative uses of a snake in a western I've seen.
A famous ex-sheriff from Texas, John Corbett is chasing Cuchillo, a Mexican man who keeps outsmarting him and escaping every time he's caught. Cuchillo is sitting with his hands tied at a desert spring when he sees a snake crawling towards Corbett. While Corbett's back is turned, Cuchillo plucks the spine of an agave plant with his toes and stabs Corbett in the back with it, then tells Corbett that the snake bit him. Corbett shoots the snake and Cuchillo convinces him to let him take care of the bite. Then he grabs Corbett's gun and escapes, letting him live because, he says, if he kills Corbett, they'll only send someone much smarter after him.
The snake appears to be a juvenile Ladder Snake, Rhinechis scalaris, a harmless species native to most of Spain.