It's probably theoretically possible to snap someones neck by twisting the head sideways, but in practice I'll bet neck muscles tense up awfully fast making it extremely hard to get the head to twist far enough.
Keep in mind that when hanging someone to snap the neck, gallows are usually built considerably off the ground, and a lot of slack is permitted on the noose, so the body drops several feet before motion is stopped and the spinal cord severed by the wieght of the body. This is because if the body didn't drop very far, the force wouldn't be enough to break the neck, and the hangee would spend a minute or more strangling to death - the neck muscles are strong enough to support the entire weight of the body.
All my fight strategy is based on deliberately injuring my opponents. -
Crippled Avenger
"It is the same in all wars; the soldiers do the fighting, the journalists do the shouting, and no true patriot ever get near a front-line trench, except on the briefest of propoganda visits...Perhaps when the next great war comes we may see that sight unprecendented in all history, a jingo with a bullet-hole in him."
First you get good, then you get fast, then you get good and fast.