Remove the Head or Destroy the Brain

A trope commonly associated with the Zombie & Mummy as well as other forms of undead - to put down the creature for good, or else render it far more vulnerable, you usually have to Remove the Head or Destroy the Brain. The head and brain are logical targets for disabling or killing an enemy, be they living or otherwise - after all, they're basically the cockpit a majority of living thing pilot their meat suit of a body from.

But what makes this subtrope of Attack Its Weak Point different from other examples - and what makes it more than just Losing Your Head - is the implication that nothing else will do the job: take off a zombie's legs and it'll drag itself after you; take off the arms, and it'll still try to worm its way towards you. Even dismemberment may not cut it completely - as long as the head's still around, that undead monster will still be moaning and groaning as it hops or rolls in your general direction, and it may or may not be joined by the rest of its body parts... but once you pulp that noggin, its remains will promptly go inert and wither away. Hopefully.

The trope also applies to some living and nonliving beings as well - some humanoid aliens and constructs that are especially durable may operate on similar logic, which only makes sense; other beings undead and otherwise can also subvert this, however. Skeletons are common candidates among the undead for subverting and playing this straight, and whether robots are still able to function on some level without their head attached depends on who's writing. And of course, not every creature will have their brain in their head.

Using this to dispatch Multiple Head Cases has varying results, depending on how much the heads control the body. Some are sufficiently disabled with the removal of one head, while more persistent types may require the removal of all of them - and then there's the Hydra Problem...

One way to make a beheading stick is to make it explode and/or land a choice headshot. Successfully doing this can render someone Deader Than Dead.

Anime and Manga

 * While the Namekians of the Dragon Ball series can be killed like any other Humanoid Alien, they possess a highly potent regeneration factor that lets them regrow lost limbs; Piccolo in particular states during the Buu Saga that he can regenerate from nearly anything as long as his head isn't damaged, which presumably applies to the rest of his people.

Film

 * Avengers: Infinity War:

Literature

 * The titular Jabberwocky is dispatched this way in Lewis Carroll's poem; both the creature and the weapon that slew it have been referenced by many works and games since.

Video Games

 * The Legend of Zelda has many a creature that can only be thwarted with the removal of its head, including several skeletal enemies (whose names usually include the prefix "Stal-"):
 * Zelda II: The Adventure of Link has the Geldarm, large centipede-like insects that block Link's path in desert levels; to defeat them, the player must attack their body, then strike at the head a few times as they lower to Link's height.
 * Big Babas in Twilight Princess are carnivorous plants that share symbiotic relationships with Deku Likes, acting as the head to their body; the latter can only be defeated by first killing the Big Baba, which allows the player to plant a bomb inside the Deku Like.
 * The Stalfos of The Wind Waker will crumble if struck enough times, leaving their head to hop around until their body either regenerates or the player hits their head enough; smashing their head with the Skull Hammer can defeat them instantly; Stalfos Knights in Cadence of Hyrule function similarly, though destroying the body's remains after collapsing them also works. This also applies to Stalchampion from Tri Force Heroes, who is reduced to a disembodied skull during its final phase.
 * Nethack:
 * The Vorpal Blade of Jabberwocky fame has a 5% chance to behead the victim upon hitting them, unless they have no head or else are intangible (e.g. ghosts, shades and vortices). This even includes nonliving monsters and multiheaded monsters such as ettins - of course, this also applies to you if you're caught on the wrong end, which is a very likely danger in the Astral Plane. And yes, it always works against jabberwocks.
 * The vorpal jabberwock is a deferred monster in the vanilla game based on the jabberwock; variants that make use of it, such as GruntHack and UnNetHack, often give the monster its own beheading attacks, though it retains the weakness to Vorpal Blade.
 * While possibly not literal, brainlessness can result from being hit by one too many brain-eating attacks by a mind flayer, which reduces your intelligence - not only is this also an instadeath if your INT drops too low, but even won't work properly, since your brain will still be gone after.

Western Animation

 * In the final season of Samurai Jack, Scaramouche manages to survive his defeat at Jack's hands as a head, and just barely manages to make it back to his master Aku in time with news that the samurai had lost his sword, which was enough to earn him his body back. Unfortunately, by the time they next encounter him, he's long recovered his sword; Aku's punishment is... rather apt.

Real Life

 * Cockroaches are subject to popular claims of being able to live without their heads, potentially subverting this trope; however, their capacity for such is exaggerated, and the trait is by no means exclusive to them. That said, a cockroach's severed head can still survive and wave its antennae for several hours, while the body still demonstrates behaviors such as shock avoidance and escape behavior.