Growing up in Eastern Kentucky where there is a very large venomous snake popluation, you learn very quickly what is poisonous and what is not. Pit vipers have a triangular shaped head which is easily recognizable from any distance. Rattlesnakes don't always rattle but that is not an inference that they are not poisonous and copperheads have a varying range of color schemes depending on the time of year. I have also been in situations where we have blasted in coal operations and discovered dens of snakes that included non-venomous and venomous in one den, something the "experts" have stated does not happen. I was also "lucky" enough to hook a cottonmouth while fishing in western TN in a lake where only the locals would attest to their existence because the "experts" denied the possibility. Improbable does not mean impossible and the important thing is to be careful, regardless of where you are.