Squirrels cannot vomit or burp because their stomachs have a one-way valve that is too strong to open backward.

This trait is found in all rodents, including rats and mice. Researchers like Dr. Charles Horn at the University of Pittsburgh found that rodents lack the brain signals needed to vomit. Their diaphragm and stomach muscles are not wired to push food upward. The barrier between the stomach and the esophagus is much thicker in squirrels than in humans. The pressure needed to force food out would likely tear the stomach wall before the valve opened. Because they cannot get rid of bad food, squirrels have a very sharp sense of taste to avoid poisons. Some squirrels also eat clay or soil to help neutralize toxins in their bellies. This behavior is called geophagy. Since they cannot burp, eating foods that cause gas can lead to dangerous bloating. This one-way digestive system is why certain poisons are so deadly to rodents.