Pit vipers have certain features that can help distinguish them from nonvenomous snakes:

Vertical slitlike pupils

Pits between the eyes and nose

Retractable fangs

Rows of single scales across the underside of the tail

Triangular heads (like an arrowhead)

Nonvenomous snakes tend to have the following:

Rounded heads

Round pupils

No pits

No fangs

Rows of double scales across the underside of the tail

If people see a snake with no fangs, they should not assume it is nonvenomous because the fangs may be retracted.