 Snake scales may be modified to form fringes, as in the case of the Eyelash Bush Viper, "Atheris ceratophora", or rattles as in the case of the rattlesnakes of North America.Certain primitive snakes such as boas, pythons and certain advanced snakes such as vipers have small scales arranged irregularly on the head.Other more advanced snakes have special large symmetrical scales on the head called "shields" or "plates".