According to The Natural Source, a site funded by Northern State University and the South Dakota Department of Agriculture, bullsnakes have long, slender bodies with pointed tails, while rattlesnakes have thick bodies and blunt tails with rattles on the end. Rattlesnakes also have an easily recognizable head that is very wide and sits on top of a narrow neck.
Rattlesnakes are known for having vertical pupils. This is different from the round pupils that are found on bullsnakes. The key difference between these two types of snake is that rattlesnakes are poisonous, while bullsnakes are not. People often confuse these two snakes because bullsnakes sometimes vibrate their tails like rattlesnakes when they are nervous or frightened. Although bullsnakes don't have a rattle on the end of their tails like rattlesnakes do, the rustling of their tails in dry grass can easily be misinterpreted as a rattle.
Despite popular myth, bullsnakes and rattlesnakes cannot mate and create snakes that look like bullsnakes but are poisonous. This is because the two snakes are completely different species. Rattlesnakes don't lay eggs. Instead, their young hatch inside of them, and they give birth to live young. This is different than bullsnakes, which lay eggs.