In AMC’s “The Walking Dead,” stabbing a zombie in the head is an efficient and stealthy way to eliminate the undead. You don’t waste valuable ammunition and you avoid attracting other zombies with loud gunfire.
When Rick’s crew plunges bowie knives and other sharp weapons into zombie skulls, those zombies instantly fall to the ground, as if the knife flipped some switch in their brain.
But that’s actually a very suspect way of stopping a zombie.
The skull doesn’t decompose the way tissue does, so even after a human has died, it would be actually be quite difficult to pierce a skull with a knife. Plus, even if you get through the skull, the knife cutting into the brain doesn’t guarantee that the zombie will be stopped.
As Nerdist’s Kyle Hill explains in his “Because Science” series, people survive horrifying brain injuries all the time. To ensure a zombie is stopped forever, it’s all about the brain stem.