Some of these pictures and descriptions may give away plot details that you might not want to know before watching the film.
I watched this because it was a Steve McQueen western, knowing that it had a snakebite scene, but it is not one of his better films. Afterwards I read that George Lucas based the name Indiana Jones on Nevada Smith, but there really is no other similarity between the two characters. McQueen is Smith who is a half Kiowa Indian hunting the three men who killed his parents. Suzanne Pleshette is a Cajun woman laborer who helps Steve McQueen and Arthur Kennedy escape from a prison camp located in the middle of a Louisiana swamp. She paddles a canoe up to where they are waiting when Kennedy capsizes the canoe and she falls into the water. She comes up saying something hit her. We see a snake swim into the vegetation. It's hard to tell what it is but the pattern looks like that of some Cottonmouths, which makes sense in that location. Later we find out she has been bitten on the shoulder and is seriously ill because of it. The venomous snake bite was just used here as a convenient way to get rid of the woman because once McQueen escapes there is no place for her in the movie.