system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does your stomach grumble when you're hungry?

Title says it all.
gpt
When your intestinal muscles contract they push stuff around. If there's food in there it doesn't make much noise; if there's nothing but stomach acid and air it'll make a gurgling sound as gas pockets move through the liquid in your guts.