The brain is essentially made up in layers and clumps lined up from the forehead to the back of the skull. So to be the most effective with your head shot, try making the bullet take the longest path through the skull therefore killing the most systems. Some of these systems maybe inoperable since infection, so shooting a zombie from the side may just destroy something they don't need. The part of the brain that controls the functions of the body like heart, lungs etc (This is for infected not "zombies" seeing as they are somehow capable of surviving with out this though it is vaguely explained if at all in the survival guide.) is located in the neck/back of the head area. Shoot this for those bleeding zombies who must eat and breathe to survive. If you have a melee weapon and still want to disconnect the brain from the body, you don't have to cut the head off. Simply use the shoulder blades of the zombie to play a little game of Doctor, Doctor (you know the game with the tweezers and the buzzers) just add a little umph and some elbow grease. Your weapon should sever the connecting organs and render the zombie paralyzed.

What not to do:
Do not shoot it from the side at the mouth. It will just loose teeth.
Do not shoot it under the earlobe or in the jaw, your bullet will merely destroy the tongue of the zombie.
Do not go for a shot that only takes out the forehead, try to get a longer vector through the skull or else it may just keep coming.




Also note: You should keep this in mind if facing a human as well. They can survive head-shots too.