I work with bull snakes in the herpetology lab at my university. I know that part of their diet in the wild can include other snakes. Here is what wikipedia says about bull snakes killing rattlers. "Bull snakes eat small mammals, such as rats, mice, rabbits, gophers, prairie dogs, as well as ground nesting birds and the young of other snakes. It is commonly believed that bull snakes will kill rattlesnakes; this possible misconception is often touted as a reason for humans not to harm bull snakes when encountering them in the wild." http://en.wikipedia.