Some of these pictures and descriptions may give away plot details that you might not want to know before watching the film.
When the movie opens we see Mel Gibson as Maverick on his horse with his hands tied and a noose around his neck with the end of the rope tied to the branch of a dead tree. One of the men who left him to hang wears some rattles as an earring. Another tells him they're leaving but it's not good for a man to be alone out there. He drops a bag full of rattlesnakes on the ground beneath Maverick and tells him "Enjoy the company." The snakes get out of the bag as the tree branch breaks and Maverick falls to the ground next to them, but for some reason, even though we see them striking, the snakes don't bite him before his horse drags him away to safety.
They used a mix of live snakes and fake snakes. The live ones look like Western Diamond-backs and Red Diamonds, and maybe a Mojave Rattlesnake, also.