Important features in snake identification include color, pattern type, length, head shape and tail characteristics. In the United States, any snake with slit-shaped pupils is poisonous, although some poisonous snakes have round pupils.
Small, medium and large are the three general categories in classification of snake length. Color varies from the relatively dull, solid color of the black rat snake to the bright display of the coral snake. Pattern types include dots, diamonds and rings. Rattlesnakes, as their name suggests, have rattles on their tails.
Even though some poisonous pit vipers have triangular heads, many non-poisonous species can flatten their heads, so this factor is only of limited value in identification.