Last night's Walking Dead and Talking Dead were great, as usual. I do have a point of criticism though. One of my pet peeves in zombie fiction is when the "death" of a zombie by way of a melee blow to the head is glossed over like it's a simple feat. The human (or vertebrate) skull is a device millions of years in the making, and it is very good at doing it's job - namely giving the most important organ in the body a practically invulnerable shelter. When zombie survivors of average strength and build stab through it with a butter knife or glass bottle or garden hoe, this obliterates my suspension of disbelief that I construct to enjoy tales of about creatures that couldn't possibly actually exist.
During Talking Dead, producer, revered effects genius, and all around awesome dude Greg Nicotero was asked by a member of the audience if Zombie skulls degenerate over time, as recently, everyone can seem to easily penetrate them, either with stabbing or blunt force. Nicotero said no. This was the one loophole that might have made these scenes (and to be fair, most zombie films and shows are guilty of this oversight) feasible. If some mysterious property of the zombie condition meant your body loses it's durability and physical constitution (along with most other abilities humans have), then I guess I can buy it. The bones are one of the last things to deteriorate in a corpse, but if whatever force animates these things changes that, I can accept it just because I've already accepted that said force really changes the rules of physics and biology (such as a thing needed some sort of fuel to propel its movements). But if bones don't go brittle in zombies in the same way that the vampires in From Dusk Till Dawn (featuring Nicotero's mentor and fellow zombie effects legend Tom Savini as Sex Machine) are explained to be (strangely and conveniently) squishy and much more fragile than a human, then alot of these scenes are downright impossible.
Now I must admit, I don't know exactly how much force is required to not just fracture, but penetrate the human skull. I haven't thought of a way to research this that won't involve the police, or at the very least, strange looks and the person backing away from me slowly. I know it's considerably more pounds per square inch than knocking down a conventional wall. Part of this is because the skull is round, and a large percentage of physical attacks toward it do not impact at a 90 degree angle. In other words, most shots will be glancing, and do a fraction of their potential damage. Even direct blows, however, find much of their kinetic energy dispersed along its round form. This is the principle behind the geodesic (or Fuller) dome structure. A martial artist may break flat boards, but if he tried breaking a hollow dome of the same (or even lesser) thickness, he would need many times more power (and hand toughness) to break it.
When Nicotero was questioned as do why the eye popping zombie along the fence... popped its eye out, he responded that the legions of zombies behind him exerted enough force with their collective weight. Again, this seems quite unlikely. This force is generated by the leaning being done, with their legs, arms and torsos. Assuming this one zombie was on his knees so that his head was inline with everyone else's shoulders, torsos, or knees (because if he's standing, his head is too high to be crushed), his skull still has more structural toughness than the other zombies torsos. I estimate dozens of other zombies near eye-popper would have to have their midsections and lower bodies ground to pulp before generating enough pressure to fracture a skull.
In conclusion, people who want to get an idea what sort of slice, stab or crushing blow is needed to kill a zombie should go to their nearest supermarket, and buy a coconut (if available), and try to penetrate that (or I suppose, one could watch the coconut scene from Cast Away with Tom Hanks). A zombie skull is larger, thicker, stronger, higher in the air (I.E. standing), in state of clumsy, sporadic movement, and is severely terrifying. Oh, and trying to bite you. If your coconut is any of these things, discard it immediately.