What happens to snakes that swallow rodents as a whole?
Almost everything the snake eats is completely digested. They have a very efficient digestive system. Things that wouldn't be digested would be the rodent's claws and hair and feathers of birds. And during digestion, the snake's intestines go into overdrive mode and expand when necessary. When the snake isn't eating, the intestines are usually dormant.

If something goes wrong though, or if the snake is threatened, the snake regurgitates everything in order to increase its mobility.