In snakes, the lower bones of the jaw, or mandibles, are not connected like they are in mammals. At the front, each mandible is attached by a stretchy ligament. The mandibles can therefore spread apart laterally, increasing the width of the mouth. The mandibles are loosely connected at the back to the skull, allowing for much greater rotation than most animals have. This is how the snake can open its mouth wider than its body. The mandibles move independently of each other, slowly inching the prey into the throat. Simultaneously, the snake’s head “walks” forward in a side-to-side motion over the prey’s body, so as the prey is levered backward the head moves forward. The process can take a while. Backward-pointing teeth help ensure the prey does not escape if it is still alive.
Swallowing is only half the battle, though, and prey must also be digested. Snakes don’t chew their food; they chemically digest it. So there is limited mechanical breakdown. Digestive enzymes can only act on the tough outside of a meal. Consequently, snake digestion can take a while, and snakes often cough up partially-digested meals.


https://www.youtube.com/watch?v=GklIPJtiXI4