The problem with that is I can think of a bunch of exceptions to that rule. Water snakes have broader bodies. Coral snakes and pygmy rattlers are pretty skinny too. Even the "red touch black, friend of jack, red touch yellow kill a fellow" rhyme only works in the southeast US. Other generalizations like head shape and pupils are often wrong too. You just need to know how to recognize 3 species of snakes and remember the rhyme. If you can identify snapper or grouper, there's no reason why you can't learn what venomous snakes look like.Recently had a snake expert tell me that a coral snakes nose will be black. He also said that most snakes that have a body like a broom stick are normally safe but any large body snakes are normally poisonous. By large body he said the body is thicker than the head.