Removing the Head or Destroying the Brain/Playing With

Basic Trope: Zombies can only be killed by means of severe head trauma.
 * Straight: Zombies can take anything you dish out, except a shot in the head.
 * Exaggerated: Chunky Salsa Rule by way of Tap On the Head.
 * Justified: the nervous system is the only system working, destroying that stops the zombie stone cold.
 * The Puppeteer Parasite nests in the skull.
 * Inverted: Zombies are Made of Plasticine except for their skulls, which are Immune to Bullets.
 * "Aim for the limbs!"
 * Subverted: A zombie is shot in the head... and just keeps on coming, its magically animated body stumbling around headless.
 * Doubly Subverted: ...however, it's as good as dead because it can't eat or detect prey.
 * Averted: Zombies can be killed like a living person, it just doesn't hurt as bad if you shoot them in the guts.
 * Deconstructed: "Center of mass" is taught so widely for a reason. One headshot's a fluke - thousands consistantly is impossible. The fact that it's a zombie's only weakness thus makes them very difficult targets, esecially at long range.
 * Reconstructed: The zombies' cerebral weak point gives vital clues to The Smart Guy about how they work, which he uses to engineer a cure for The Virus.
 * Parodied: Zombie heads are like soufflés; the slightest disturbance causes them to collapse into goo.
 * Enforced/ Necessary Weasel: "Look, it's a zombie movie. If they can be killed by normal means, it's just not a zombie movie."
 * Lampshaded: "All we know about them for sure is they smell really, really bad. Always go for a headshot, just in case."
 * Invoked: Cranial Processing Unit
 * Defied; "You think cutting off my pretties' heads will stop them? Bwahaha, my potent magicks would sustain them even as a shambling bag of flesh and bone!"
 * "We have identified a new type of Creature, which has all but completely replaced the standard 'zombie'. They have evolved a thick, bulletproof carapace covering everything from the crown of the head, to the shoulders and collarbones (except for the lower mandible), which is filled with cerebrospinal fluid, like a second skull. It has been proven to deflect everything from buckshot to minigun rounds. Headshots and decapitation are now useless tactics."
 * Discussed: "If horror movies have taught me anything, it's you have to shoot a zombie in the head to kill it."
 * Conversed: "Oh, gee, how will they ever discover the weak point of these mysterious walking corpse-like beings? Maybe, just maybe it's their head -you know, like every other zombie movie ever made"

Aim for the head!