How Do You Tell The Difference Between A Poison And A Non-poison Snake?

First of all, there's no such thing as a "poison" or "poisonous" snake.  A poison is something you have to swallow or breathe in for it to harm you.  Chlorine bleach is a poison, for example.  No snake as poison; you can eat any snake.  Some snakes have VENOM, which is different from a poison in that it is always manufactured in the glands of some animals, and needs to be injected into the body to cause harm.  Bees and sting rays also are examples of animals that have venom.
In the United States, all of our venomous snakes, with one exception, have vertical slits for pupils, like a cat's pupils.  All of our non-venomous snakes have round pupils, like those in our own eyes.  Most of our venomous snakes are in the pit viper family, and have very large heads that are shaped like an equilateral triangle, widest at the rear where the neck is connected.  The neck itself will look rather skinny in comparison to the head.  Pit vipers also have an opening on the face, between each eye and nostril, that looks like an extra nostril.  This is the infrared-sensitive "pit".  Rattlesnakes, Cottonmouths, and Copperheads are all pit vipers.  The one exception to this is the Coral Snake, which is a member of the Cobra family.  It has round eyes and a small head, like a harmless snake.  Coral Snakes have rings around their bodies in red, yellow and black.  In a Coral Snake, the red and yellow rings always touch, but in a non-venomous Milk or Scarlet King Snake, the red and yellow rings are separated by a black ring.
When in doubt, the best advice is to LEAVE THE SNAKE ALONE!  Most people who are bitten by venomous snakes get bitten while trying to harm the snake.  Never try to pick up a snake if you're not certain of what kind it is.

Call animal poison center