system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why do the normal bacteria in our mouth attack out teeth and gums,but those in other parts of the body do not attack those parts?
gpt
The bacteria in your mouth are like junkyard dogs. They are there because they are good at breaking down things that are coming into your body, but they are also aggressive and not well-trained. They'll stop someone from stealing stuff from you, but they might also bite your friend they've never met before.

Also, there are other bacteria in your body that are even worse. The stuff that lives in your intestines is like a pack of wolves. As long as they're contained in your guts, they are great at breaking down almost anything that comes through. If they ever get out, though, they'll try to eat everything they come across.