It is most common in boas, pythons, tropidophiids, colubrids and elapids of the genus "Acanthophis". In others, such as the colubrids and elapids, they are enlarged. Until recently, colubrids were basically colubroids that were not elapids, viperids, or "Atractaspis". Like nearly all colubrids, rat snakes pose no threat to humans. Good numbers of smaller colubrids can be taken as well, especially garter snakes. Like some other colubrids, they are commonly called racers. The pupil of the eye is round, a feature shared with most other colubrids. It is the second largest subfamily of colubrids, after Dipsadinae. The head is distinct from the rest of the body, as in many other colubrids. Like most colubrids, if harassed they will vibrate their tail rapidly.