system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What determines whether gas exits your body as a burp or a fart?

Thank you.
gpt
A burp is built up air in your stomach. Only by drinking, swallowing or eating will you get air in your stomach. You stomach isn't made to process air or gasses and sends it back where it came from: your mouth.
Farts are gasses given off by bacteria that decompose the food in your intestines. When they take out valuable vitamins and minerals from your poop they give off gas in return.