How do snakes defend themselves when they are scared or threatened?

with venom and camouflage

Snakes defend themselves by spitting venom, biting, or excreting a foul stench.

Some snakes like the spitting king cobra would however non venemous snakes like the corn snake (Elaphe Guttata) don't spit as they have no venom to spit at the enemy. When a snake spits it is...

yes they spit and bite

Many many things, nearly every thing that moves that is larger then it and does not smell like food. many things that move or that is larger than it is or does not smell like food