While the food that is in your stomach is getting mushed up by the peristalsis, it is also getting turned to mush by a chemical called hydrochloric acid.
This acid is so strong that if you had a glass of just hydrochloric acid and you touched it with your hands, it would burn your skin.
Luckily your stomach has this gooey slimy stuff in it called mucus all along the walls of your stomach that protect it from the acid.
(from: wikipedia - stomach)
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