Claw

In tetrapods, claws are made of keratin, and consist of two layers: the unguis, which consists of keratin fibers perpendicular to the direction of growth arranged in layers at an oblique angle, and the subunguis, whose grain is parallel to the direction of growth.

A nail is homologous to a claw, but is flatter and has a curved edge instead of a point. A nail that is big enough to walk on is called a hoof.

A talon is the claw of a bird of prey.

Every so often, the growth of claws stops and restarts, as does hair. In hair, this results in the hair falling out and being replaced by a new one; in claws, this results in an abscission layer, and the old segment breaks off. This process takes several months for human thumbnails; cats are often seen doing it on wood or on boards made for the purpose.