Your diaphragm, a big, flat muscle located under your lungs, pulls down to create a void in your lungs. Air then fills that void which is you “breathing in.” When your diaphragm pulls down, it runs into your stomach, liver, etc. Those bois have to move down/out/backwards to make room for the diaphragm to lower. That’s why your stomach might look like it’s filling with air, when really it’s just moving out of the way for your lungs to fill with air.
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