Snakes are able to swallow prey three times their size because they have a very strong jaw. The snake bites the prey and then uses its powerful muscles to crush the vertebrae in the backbone. This causes the prey to choke and suffocate. In some cases, the snake may swallow the prey whole.
In this situation, the snake has to crush the prey with its jaws. The stronger muscles in their jaw can allow them to break through bones and eventually grind their way out.