The jaws of the snakes are not fused together. That means that unlike our jaws, snake jaws are not connected at the back of their mouths. This makes it possible for them to eat very big meals, bigger than their own heads! That would be like you swallowing a whole watermelon!
If you had your mouth full of a watermelon, do you think you could breathe? Not likely! Snakes can. They have a little tube at the bottom of their mouth that comes out far enough to get air when the rest of their mouth is full.