The small claw-like hind-limb remnants of boas and pythons are called pelvic spurs.
Pelvic spurs are external vestiges of the ancestral hind limbs that snakes lost during evolution. They are located near the cloaca, at the base of the tail, and are especially visible in many boas and pythons. In males, the spurs can be used during courtship to stimulate or grip the female.
These structures are not functional legs. Their presence is evidence that modern snakes evolved from limbed ancestors, although the precise pattern of snake limb loss remains an active subject of evolutionary research.
Not every living snake displays obvious spurs. They are most familiar in boas and pythons, while many other snake lineages lack visible external remnants.