Some of these pictures and descriptions may give away plot details that you might not want to know before watching the film.
Charles Bronson plays Chato, a man of white and Apache Indian ancestry, who killed a sheriff in self defense and is chased by a posse made up mostly of racist morons who think all Indians are animals, led by Jack Palance, who wears his old Confederate Colonel's uniform.
After some of the men in the posse rape Chato's wife, he stops hiding from them, changes into a loincloth, and starts chasing and killing them one by one, while also watching them kill each other, getting the sort of self-righteous revenge that you came to expect to see in Bronson's later films. To kill one of the men, Chato suddenly appears on a ridge above him and throws a live rattlesnake down at him. The snake lands on his neck and bites him on the cheek. The man struggles then flings it off and it crawls away. He is spared the agony of a slow snakebite death because Chato shoots him.
Both live rattlesnakes we see look like Western Diamond-backed Rattlesnakes, which are often used in movies. The Dead and skinned snake also looks like a WDB. The snake Chato throws is most likely a fake snake, or a dead one at least.
At his campsite, Chato sees a rattlesnake. He kills it with a large knife, skins it, cuts off the rattle, puts the rattle in the snake skin and wraps it up in a ball that he puts in his pocket. Then he roasts the meat on a fire and eats it. Later he gives his son the ball, which rattles like a musical instrument when he handles it.