The snake in this episode's titular scene is a real rattlesnake.
The original script called for Chet to get bit by the snake. But, producers looked it over and decided that either Roy & John should get bitten. Things went back and forth, finally they decided on Johnny. Randy was bitten for real, and it did hurt him, though the snake had no venom. Sharp listeners can even hear Randy's legitimate pain response under his breath saying "Damn it."
As the bulldozer goes down the hill, distant shots clearly show the operator is wearing a full face mask. Going back up the hill, the operator is wearing the full face mask.
When Johnny goes back for his walkie talkie and gets bitten he manages to fling it over the top of the car and then has it when he gets situated on the ground.
Randy Mantooth was reported to have stomped on the snake that actually bit him in a fit of rage.