And the easiest way to distinguish between venomous/non-venomous is simple education. There are 4 types of venomous snakes in the US - 3 (rattlesnakes, cottonmouths, and copperheads) are pit vipers possessing heat sensing labial pits on the snout. Nothing else really looks like rattlers or copperheads out there, though plenty of non-venomous snakes will rapidly shake their tails when feeling threatened to deter predators. Cottonmouths can be a little tricky since there are so many species of water snake out there too, and they're all meaner than hell and more than willing to stand and fight if given the chance. Cottonmouths generally don't want to bite, and the threat display of a gaping mouth is just that. The best way to tell the difference is that cottonmouths will have a distinct and thinner neck whereas water snakes necks and heads seem to be one. They (cottonmouths) also have a dark band running through their eye and aren't quite as tapered as water snakes, though the latter will puff and flatten themselves out in a defense display. Coral snakes make up the forth group, and they're the only terrestrial elapids in North America. Their venom is extremely potent, being of the same family as cobras and mambas, but they are uber secretive, possess tiny fangs, and the chances of being bitten by one are astronomically small, even if you're harassing the snake like an idiot. Red on yellow kill a fellow - easy as that.