I think that the shock of a bullet going through the neck sends enough shock to shatter a main artery or the spine, So a dead on shot is not necessary like it would be with a bow. I'm sure you could just nick the animal and it would get away but you can do that aiming for the vitals too. I have never taken a neck shot but I have heard if you shoot them right where the base of the neck meats the shoulder that the shock will send them straight down even if it is not a direct hit to the spine. A guy on another forum said he tried this once and he has shot every deer this way since then and every one of them dropped in its tracks and didn't move another muscle.