After a rattler bites its prey and lets the prey run away. By the time the rattlesnake finds the prey, it will be half digested, because of the venom it injected. This makes it really easy for the snake to eat. They eat their prey head first, by unlocking their jawbones. They are completely helpless while they are eating and are not able to defend themselves.
Rattlesnakes can bite without injecting venom.
They usually save their venom for their prey. The king snake is totally immune from the rattlesnakes venom. Rattlesnakes use their rattle as a warning to others to stay away. The king snake is deaf though, and can't hear the rattle noise. What is really strange is that rattlesnakes know this, and will stop rattling once they realize that it is a king snake they are trying to scare.