"The strangest trio ever to track a killer. A fearless, one-eyed U.S. marshal who never knew a dry day in his life... a Texas ranger thirsty for bounty money... and a girl still wet behind the ears who didn't care what they were or who they were as long as they had true grit."
Mattie Ross falls into an old mine shaft next to a corpse. Inside the rib cage and under its clothing, a bunch of rattlesnakes are hibernating. Disturbed by her fall, the snakes start to move and she beats them off with a branch. One snake bites her on the hand. John Wayne grabs a rope and swings down into the mine with his guns blazing, shooting snakes right and left cowboy style. Then he puts chewing tobacco on the wound and wraps it and rides her off to a doctor. I find all of this to be plausible, despite the rope-swinging gun-slinging theatrics. Snakes do hibernate in groups underground during winter to keep from freezing and during summer to keep from overheating, and if threatened by a girl with a stick, a rattlesnake would surely strike to protect itself. And it's only the one snake she gets too close to that bites her, the others just disperse to get away from her. "
Most of the snakes we see here are live - probably Western Diamond-backed Rattlesnakes.
Another movie was made from the book in 2010, including the rattlesnake scene.