I researched a little as to whether snapping someone’s neck would actually kill them as quickly as it is often portrayed in the movies.  The consensus seems to be that it’s possible, but it isn’t as easy and precise and immediate as Hollywood would have you believe.   It seems that the attacker would have to be exceptionally strong and would need to hit exactly the right spot, and even then, the victim wouldn’t die instantaneously.  Of course, since we’re in a comic-book reality here, we can believe that VIXX really is that strong enough to do the deed.