Pit vipers have certain features that can help distinguish them from nonvenomous snakes:
Vertical slitlike pupils
Pits between the eyes and nose
Rows of single scales across the underside of the tail
Triangular heads (like an arrowhead)
Nonvenomous snakes tend to have the following:
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.