system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Sometimes if you drink enough water you can feel it slosh around in your stomach. Why do we feel it under certain circumstances even though there are always contents in your stomach, like stomach acid?
gpt
If you haven't consumed anything in a long time, your stomach will be mostly empty. Because it's empty, it's being sqished together tightly by the rest of your body. There isn't even a lot of acid in there or anything.

If you fill it, the walls of the stomach stretch, and more gastric juices are added. If you eat or drink quickly, a lot of air will also enter the stomach. That's usually where the loud sloshing comes from - the waves you create on the ocean of your stomach. A very stretched out stomach full of liquid, might wobble around a bit, due to the momentum of the water etc.

Pretty much like a water bed.