Identifying pit vipers Pit vipers have the following features, which help differentiate them from nonvenomous snakes: Arrowhead-shaped (triangular) heads Elliptical pupils Heat-sensing pits between the eyes and nose Retractable fangs A single row of subcaudal plates extending from the anal plate on the underside of the tail Coral snakes in the US have round pupils and black snouts but lack facial pits.