Most people know that snakes can open their mouths extremely wide, but how do they do it? It is a common misconception that snakes can dislocate or detached their jaws. This is not true.
Snakes have a special split lower jaw that is attached by a stretchy ligament. This allows the lower jaws to stretch horizontally. Their lower jaw is loosely attached by the quadrate bone and ligaments at the back of their skulls, instead of being attached at the sides like most mammals. This allows snakes to open their mouths up to 150 degrees
Check out this snake opening and closing its mouth.
Eye of the Wild Photography 