Snakes do smell. That's what all that tongue flicking is about. They don't use their nose, they have a Jacobson's organ on the roof of their mouth and the tongue brings in particles in the air and then touches the Jacobson's organ.
I have garter snakes and rat snakes. Never seen a large one. Neither are venomous. Garter snakes eat grasshoppers and rat snakes eat mice. My chickens will kill the small snakes, but I don't think they would tackle a big one.
Moth balls are poisonous, so keep them away from your pets.