Many mammals, birds, and reptiles have a dewclaw on their foot, which is a finger that is still present in some creatures (including some extinct orders, like certain theropods). In digitigrade or unguligrade animals, it frequently develops higher on the leg than the rest of the foot, preventing it from touching the ground when the animal is standing.
The name alludes to the dewclaw’s purported propensity to brush the dew off the grass. The dewclaws on dogs and cats are located inside the front legs, like the human thumb, which is an evolutionary cousin. While many animals have dewclaws, several species, including horses, giraffes, and the African wild dog, have not.