Bile reflux into the stomach. Bile and food mix in the duodenum and enter your small intestine. The pyloric valve, a heavy ring of muscle located at the outlet of your stomach, usually opens only slightly — enough to release about an eighth of an ounce (about 3.75 milliliters) or less of liquefied food at a time, but not enough to allow digestive juices to reflux into the stomach. More @Wikipedia
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