Cottonmouth

The "white tail" has nothing to do with this being a copperhead vs a cottonmouth. The tip of the tail is actually green, and both copperheads and cottonmouths have it as juveniles. They use it to wiggle around above leaf litter while they sit still, and the bright tail mimics a worm. The prey come to eat the worm, but instead the snakes eats the prey.