How do you determine if a snake is venomous or non-venomous in Pennsylvania? There are three main characteristics to look for when determining if a snake is venomous or non-venomous in Pennsylvania: 1. Venomous snakes have small necks, and non-venomous snakes' heads and necks tend to be the same width. 2. Venomous snakes have elliptical pupils, and non-venomous snakes have completely round pupils. 3. Venomous snakes have a rattle or single scales on the tail, and non-venomous snakes have split s