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"Clint Eastwood…the deadliest man alive...takes on a whole army with two guns and a fistful of dynamite!"
We see a rattlesnake in an abandoned building in the Mexican desert. (It's a fake snake with strings holding up its head and its tail and wiggling the rattle.) As always, we hear rattling sounds. Clint Eastwood holds his boot out so the snake will strike it and when it does, he swings his big knife and cuts its head off. Now the snake we see is a real but dead Mexican rattlesnake of unknown species. He gives the body of the snake to Sara to save and cook for dinner.
Sara takes the snake then goes to hide from some approaching French soldiers. When one of the soldiers comes close to where she's hiding, she shakes the snake's rattle. This works. When the soldier hears the rattling sound he turns around afraid to go any farther.
The snake used in this scene looks completely different from the first one, even though it's supposed to be the same snake. It's a real dead rattlesnake, but of a different species. When we see Sara holding the snake again, it looks the same as the first one. (This is frustratingly sloppy.)
Later we see Sara and Eastwood eating the snake for dinner.