Larry, I've seen the exact behavior you're describing many times in the past, and it does seem cornsnakes are more prone to this behavior, than many others, although I don't know quite why. Boa and Python skulls are somewhat different than colubrid skulls in their bone structure, one, or the other even has an "extra" bone that the other does not, but I can't remember which one now, off the top of my head. The independently moving mandibles(lower jaw bones) are connected to the joint by loose "elastic-like" ligaments.

Below, is a diagram and text that better depicts the dynamics of the movement than I can describe.

hope this helps, ~Doug

Depicted above is a side view of the skull of a Burmese python, with those kinetic joints that are visible labeled. The joints in red are highly mobile, those in green are slightly mobile, and the joint in blue, while not mobile in most snake species, is highly mobile in the African Egg-eating Snake.

The red joint A is the joint between the madible and quadrate, and is analogous to the joint in the human (and other mammal) jaws. The joint above it, labeled B in red, is the joint between the quadrate and the supratemporal, which is also highly mobile in most directions, and adds another joint to the jaw, allowing wider gape and greater jaw flexibility. The red joint C, located beneath the eye socket, is the connection between the prefrontal and maxilla (upper jaw). This allows the maxilla and its teeth to pivot in the plane of the photograph, and while it does not increase gape, it does facilitate the complex action by which the snake draws prey into its mouth.

The green joint A, above the eye socket, is a joint between the frontal and nasal bones, which allows the snake to slightly upturn its nose, slightly increasing gape and assisting in swallowing. Green joint B allows the lower jaws to bow outwards, further increasing the gape.

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"Better to be silent and thought a fool, than to open mouth and remove any doubt!"

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