system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How come a venomous animal is not affected by its own venom?
gpt
Well they don't bite themselves for one, and venom is a protein which is designed to react with cells in a specific way - usually by creating blot clots and melting the walls of cells. Because the venom is specifically developed to work on certain cell structures, the snake just has to store the venom in a cavity made of a different cell shape.

To be honest though, the same thing applies to humans. If you bit someone really hard, enough to rip the skin and draw blood, they could be at risk of a seriously bad infection without strong antiseptic (especially if the biter eats loads of meat).  
The bacteria in your mouth is dangerous if introduced into the bloodstream, but it's perfectly safe in your (or anyone else's) mouth.

PS: By the way, there are some interesting properties of venom due to the way it reacts with cells. For example some snakes have venom designed to switch off neurons in your body *and nothing else*. As the venom only works if injected into the bloodstream, some people have been known to drink cobra venom to experience hallucinogenic effects.