The vast majority of people who've lost a limb can still feel it — not as a memory or vague shape, but in complete lifelike detail. They can flex their phantom fingers and sometimes even feel the chafe of a watch band or the throb of an ingrown toenail. What causes these phantom limb sensations? Joshua W. Pate explains how the brain reacts to a missing limb. [TED-Ed Animation by Kozmonot Animation Studio].