neck brakes or dislocations can obviously not be practised in the dojo, unless with great control and caution, but my sensie used to be a certified chiropractor and i often have trouble with my spine and neck. He often does diferent stretches or drops to put my back into place. Often he stretches the spine so that discs can slot back in, usually with a nice crunch sound especially when hes fixing my neck. He has shown me lots of different ways in which the neck can be dislocated and even broke.
It isnt just in the movies it can be done actually with some ease in real life. Especially when you drop the person by a sweep etc so that their body drops in the opposite direction to the one in which the neck is being twisted to. I wont go into detail of techniques for obvious reasons.
Going back to P Carneys question can a neck break kill?
leaving uke paralyzed could be done with out much effort at all and yes neck brakes can be lethal and lead to a fatality if the right technique is applied. Their are also several main muscle and nerve groups that would be destroyed also leading to death. All the bodys nerves connect to the spinal cord, and there are 31 pairs of peripheral nerves that extend out between each vertebrae.
When exploring your katas their are several applications of neck breaks along with droping them by your lead stance leg, have a look.
[This message has been edited by martinnitram (edited 01-20-2002).]