For them, the lower jaw cannot move forward and has very limited side-to-side motion. The jaw on a cat is a simple hinge joint that lies on the same plane of the teeth; the hinge pivots. It's a lot like your knee joint.
When the jaw of a carnivore closes, the blade-shaped teeth at the cheek slide past each other and that's what allows them to shear meat off of bone. As the jaw moves, the temporarilis muscle triggers the movement of the jaw.
For herbivores, conversely, the chewing action involving forward and backward and side-to-side movement of the lower jaw pushes food back and forth into the grinding teeth - with the help from tongue and cheek muscles. This is a brilliant design that lets herbivores mechanically break down the cell walls of plants.
Meanwhile, a carbohydrate-digesting enzyme - sailvary amylase kicks into action and breaks down starchy carbohydrates. Cats don't produce salivary amylase.
So as we travel along the path of food making its way through a cat - before we even GET to the stomach and intestines - already our cat's physical makeup and biology is telling us about their carnivore status.