Graphic: Thomas Porostocky 1. You may not have marbles for brains, but your ears are filled with rocks — tiny calcium carbonate crystals called otoconia. Ear rocks, as the American Hearing Research Foundation calls them, help you maintain balance and sense gravity and linear acceleration. But they can also cause vertigo if they fall into the wrong canals in the inner ear.

2. Sugar is tasted twice — once in the mouth and again in the gut. The taste receptors T1R3 and Gprotein gustducin register sweetness on the tongue. In August, researchers at the Mount Sinai School of Medicine announced the discovery of these receptors in the intestines. When activated, the gut-based sweet-sensors promote insulin secretion to regulate appetite.

3. In addition to the five traditional senses, there is, of course, proprioception: an awareness of where the body is in space from moment to moment. This sense is more acute than you might first think. Consider: Recent research suggests that right-handed people monitor their dominant hand visually but keep track of their left hand using proprioception.

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