Horses get chestnuts because they are vestigial remnants of toes from their ancient ancestors. Chestnuts are small, callous-like growths found on the inside of a horse's legs, above the knee on the front legs and below the hock on the hind legs. They are made of keratin, similar to human fingernails, and serve as evolutionary evidence of the transition from horses having multiple toes to a single hoof. Though chestnuts no longer serve a clear biological or functional purpose today, they provide insight into horse evolution. Some research suggests they might have once played a role in limb positioning or sensory feedback, but currently, they are primarily considered harmless anatomical features. Each horse’s chestnuts are unique and sometimes used like fingerprints for identification.