Logan: I'm gonna cut your goddamn head off. See if that works.
When a character or group is lauded to be immortal, indestructible, or otherwise unkillable, oftentimes one of the few if not the only things they are not immune to is decapitation. This could be a reveal, it could be known from the getgo as "the only way to kill them"; or, as in the quote above, it could be in-universe speculation which may or may not get put to the test.
The reason for the prevalence of this trope, particularly of the latter form, probably has its roots in the Rule of Perception. An audience can swallow a character being shot full of bullets or losing a gallon of blood and shrugging it off, even when there isn't a good reason for it. And the removal of vital organs, up to and including the heart, is still conceivably survivable because hey, they can just grow a new one! After all, one can survive a few seconds with no heart even in real life, so as long as you can regenerate within that time span you're good, right? But decapitation crosses the line from "should be dying" to "already dead by definition," and you have zero time to heal.note In the minds of viewers and characters alike, you just can't be alive if your head is not attached to your neck, and it takes more than a Healing Factor to explain how you can be.
Removing the Head or Destroying the Brain is a specific subtrope for the undead. That said, in general beings who are "already dead" have a higher chance of averting this trope than those who aren't. Don't even bother trying this on Dem Bones, unless your aim is comedy. Vampires are an exception, however, as decapitation has long been a stock method of killing them. When this trope doesn't apply to a robot, it's likely because of a Cranial Processing Unit.
When cutting something's head off doesn't kill it, it's Losing Your Head. See also Chunky Salsa Rule and Boom, Headshot!. Contrast Hydra Problem, where removing the head is (without other aid) a bad idea.
- In The Twelve Kingdoms beheading is one of the certain ways to kill an immortal (the others being cutting the body in two and use of special enchanted weapons), and is shown to be the preferred method in executions. In example, this is how King Chuutatsu, Queen Kekai and the kirin Hourin are killed, with the "bonus" of having the leader of the rebels doing this "deed" show up in front of Kekai and Kourin (and Sole Survivor Shoukei) carrying Chuutatsu's head in his hand.
- Subverted with Hidan from Naruto. Asuma thinks it'll work and cuts it off, but all it does is keep Hidan from controlling his body and Kakuzu can re-attach it. Shikamaru later blows him up to the point where the only part left is his head. Hidan cusses him out. Shikamaru buries the still-living and near-immortal head in a hidden grave where no one can ever retrieve it. Rather weirdly, the Konoha ninja never try decapitation on his equally immortal partner Kakuzu — they just destroy each of his five hearts, one by one and with a great deal of effort.
- Averted in Ninja Scroll: Jubei thought Gemma was dead from this, but he reappears with a faint scar around his neck.
- Berserk has Guts fighting a monster that can regenerate as long as its head is intact...which it brags about to Guts.
- Mermaid Saga. Not the only way to kill an immortal, but the most effective and most attempted.
- In Magical Record Lyrical Nanoha Force, this is one of the only ways you could kill an Infected. Anything else will just be healed off with ridiculous ease.
- Most awakened beings in Claymore will die easier if connection between brain and body is removed, generally by decapitation. Semi-averted by one, "Bloody" Agatha, whose connection ran through her hair and neck was used only as a distraction. Fully averted by Europa the Lazy and Priscilla, the first is able to survive being decapitated in her human form and she uses this ability to play dead, it apparently fits her personality, her head can then transform in her true awakened form, Priscilla goes even further as she survives having her head cut in three pieces, her insane Healing Factor just reconnected the pieces of her head together.
- Abyssal Feeders can regenerate indefinitely, making destruction or removal of the head the only means of stopping them.
- The Immortals in Blade of the Immortal.
- The only way to kill a Euphoric in Speed Grapher is to either remove his or her head or severely damage it.
- L-elf from Valvrave the Liberator theorized that this is one of the few ways to kill a Magius.
- Mobile Fighter G Gundam states that the Gundam Fight Internal Regulation, "A gundam whose head section has been destroyed is disqualified". In other words, the loss of their gundam's head is the only damage that their pilot is not allowed to repair or replace.
- In the French series Zorn And Dirna, Death is trappped in a magical mirror, and now every single living creature is fated to age forever, unless the spinal column is severed, in which case the dead one's soul goes into the killer's. It is specifically mentioned that butchers have adapted by developing the skill of removing meat from an animal without cutting the spine.
- In X-Men, a 90s plotline involved the "Xavier Files", which were basically Professor Xavier's Batman-esque contingency plans for the best way to kill any of the X-Men (including himself) if they turned evil. For Wolverine, the only sure way to overcome his Healing Factor was said to be decapitating him and quickly removing the head from the vicinity of the body (and even this would only really apply when the adamantium had been removed from his skeleton, as with it there's no known substance strong enough to cut through Wolverine's spine).
- The same rule applies to anyone with a healing factor from Logan's and Sabretooth's families. While Deadpool's healing factor is derived from Wolverine, it's been established that it doesn't work on him.
- In Demon Knights a vampire army besieging the protagonists can only be defeated by removing the head or destroying the heart.
- Dracula is vanquished several times in The Tomb of Dracula and Dracula Lives!, but since his head is never removed afterwards to make his death permanent, he always manages to return.
- In A Man Like No Other, the only way to kill President Snow/the Maestro was for Thor to knock his jaw off with Mjolnir followed by Katniss shooting an explosive arrow into his mouth to blow up his head.
- In the sequel, Falling Hope, Rising Threat, this also applies to how Anya (the new She-Hulk) and Johanna Mason (AKA Bloodaxe) kill the Abomination.
- In the Highlander series, beheading is the only thing that will kill an Immortal. The best way to behead an Immortal is with some variety of blade, hence all the Sword Fights that Immortals get into in the series. The question of whether this is the only limit to their immortality is usually glossed over.
- The Mummy Returns: The only way to kill an Anubis Warrior is by cutting off its head.
- In addition to the page quote, X-Men Origins: Wolverine uses this on Weapon XI. This is shown in the movie as being the only way to kill anyone with a Healing Factor. It doesn't work, in this case; The Stinger shows Weapon XI's body crawling over to reattach his head.
- Horribly subverted in The Thing (1982). Decapitation does absolutely nothing to the Thing. When its head is removed it acts as an independent organism and tries to escape.
- Skulduggery Pleasant:
- Skulduggery and Kenspeckle reference this when talking about vampires in book 2. "Decapitation is effective against most things." Sometimes brought up as a running joke when vampires are mentioned.
- Mistborn: The Original Trilogy:
- Played with with The Lord Ruler. He's lauded as an immortal god, and it's common knowledge that "decapitation only irritates him," so nobody ever tries this. It's also one of the many things he claims to have survived in a Badass Boast while fighting the heroes. However, the source of his agelessness, once revealed, makes one wonder if this was actually true, and according to Word of God it was a big fat lie.
- Decapitation kills the Steel Inquisitors, who are otherwise almost impossible to beat — although it's usually easier to just pull out the spike in their backs, which also kills them.
- In Brandon Sanderson's earlier work, Elantris, Elantrians are most reliably killed by beheading. Anything less will simply leave an unhealing, eternally-hurting wound. Burning also works.
- The short story Dragon Reserve, Home Eight by Diana Wynne Jones features "hegs," people with superhuman abilities including being able to "mind read, kindle fire or more objects at a distance, heal or kill by use of mind alone, survive shooting, drowning, or suffocation..." By law, once discovered they are executed by beheading, which is the only thing they cannot survive.
- In the Keys to the Kingdom series, beheading can kill a Denizen, but their heads have to be separated from their bodies for some time, or throwing dirt in the neck stump apparently usually works.
- Played for Laughs in Terry Pratchett's Carpe Jugulum, in which vampires from different areas of uberwald have to be dispatched in varying ways (lemon in the mouth, nail through the knee, hide his sock) but all involve cutting off the head (which, conveniently, also works on people).
- The Brollachian from Shadow Keep is a part ogre part octopus brute that feels no pain and can regenerate missing limbs and chunks of flesh. However, Maryld stated that he can be slain if beheaded, but the heroes never get the chance of trying this on it.
- The only way to successfully kill a vampire in the Mercy Thompson series is to stake them, decapitate them, and then burn both the head and body to ashes.
- In Vampire Academy, there are three ways to kill the Strigoi: staking, beheading, and burning. Due to this, guardians usually carry stakes only, and no guns.
- In Shadow of the Conqueror, this is one of the only sure ways to kill a Lifebinder, as their Healing Factor will heal nearly any injury (including lost limbs) as long as they have access to enough Light.
- Charles, the vampire villain of Elaine Bergstrom's Shattered Glass. Since her vampires, who belong to a naturally evolved nonhuman species, have such a strong self-preservation drive that they literally cannot commit suicide, Charles commits an escalating series of gory murders to induce his brother, Stephen, the "good" vampire of the novel, to kill him in a vampire version of Suicide by Cop.
- Heroes: It's stated that characters with a Healing Factor can't survive decapitation, although it's never actually shown. The more commonly referenced means of taking one down is by shooting or stabbing a very specific point in their brain, but that only works temporarily; if the object is removed, they will still heal. Not so, allegedly, for full decapitation.
- When Sylar gains the ability to shapeshift towards the end of the series, he makes use of it to move this weakpoint to another point of his body, thus making it impossible to hit: chances are that with this new power, it's not a stretch to assume that he could move the rest of his brain somewhere else in his body, allowing him to survive decapitation as well.
- On Supernatural:
- This is how the "unkillable" Leviathans are finally defeated. It still doesn't actually kill them but it incapacitates them until their heads crawl back over to their bodies, a problem solved by simply putting the head in a box. It seems that in this case, removing the head doesn't work, but destroying the brain does.
- This is sometimes the case with run-of-the-mill monsters, depending on species.
- Subverted in Torchwood: Miracle Day. Jack Harkness suggested cutting off the head of an assassin who is being kept alive by the Miracle (despite being burned to a crisp). The authorities try it, and he's still alive. Jack himself also subverts this in all post 9th Doctor appearances except the aforementioned Miracle Day.
- "Braining" always worked on Star Trek: The Original Series.
- Decapitation is one of the few ways to kill a vampire in Buffy. They instantly turn to dust once their head isn't attached to their body. Angel brings up another caveat; vampires have a Healing Factor but their brain won't heal from some injuries, meaning they could be left brain-damaged for all eternity if something happened to it. This is mentioned, but it never comes up in the actual story.
- Subverted with Lorne (and presumably other Pyleans); in order to kill one of their kind, you must decapitate them and dismember the body. Lorne's family saved him (grudgingly) by switching his clothes with that of another decapitated body awaiting dismemberment.
- In Moonlight vampires follow White Wolf rules. Eventually it turns out that the guillotine was invented because many French aristocrats were vampires.
- In Doctor Who this is implied to be one of the few things that will immediately kill a Time Lord (although some Expanded Universe media suggests that the Time Lord would just begin regrowing a new head during regeneration unless both hearts are destroyed). Aspirin may or may not be another.
- Greek Mythology:
- Averted with the Hydra from Greek Mythology. It started off with nine heads, and every time one was cut off it would grow two in its place. Hercules finally defeated it by cutting off its heads and having a friend cauterize the stumps with fire to prevent them from regrowing. However, it had one immortal head; and presumably that was undecapitable. Once the others were destroyed, Hercules just buried that one.
- The weakness of Medusa, the gorgon. While her two sisters were immortal, Medusa had a mortal neck covered in metallic scales which could be severed by means of an adamant blade, which the hero Perseus used to kill her.
- One guest on Plumbing the Death Star suggests Comic Book/Superman could be killed by decapitation, which confuses Jackson since, as he puts it, he didn't know Superman was a vampire. Zammit and Jackson then list off other vampiric qualities Superman has, like only being able to come in if you invite him to sucking the blood of the innocent to having to... count any panties dropped on the floor? They go farther and farther on the tangent until they read from Dracula, realize decapitation wouldn't kill Superman, and decide to move move on from Vlad Kent.
"'Oh, creatures of the night, what beautiful music they make, I have to save Metropolis!' Superman!"
- Subverted in Dungeons & Dragons; Vorpal weapons instantly decapitate enemies on a critical hit, but some enemies either don't have heads to remove, or aren't inconvenienced by it. Specifically, the latter includes monsters with regeneration (though Ogre Mages need to reattach their heads within ten minutes), most Constructs, and Undead (save for vampires).
- Incidentally, killing a vampire (in 3rd edition) requires staking them in the heart and then cutting off the head.
- Pathfinder has Vorpal weapons that are much likes the ones in Dungeons & Dragons. In addition, Pathfinder also introduces the Jabberwock creature, which has a particular fear of vorpal weapons; striking one cause it to become temporarily shaken.
- Decapitating a Harrowed from Deadlands doesn't kill them. It reduces them to fully conscious but helpless heads.
- In the French RPG Trinités it is usually the surest ways to kill the eponymous beings for good.
- Decapitating an ork in Warhammer 40,000 won't actually kill it (at least for a little while — some "doks" have been known to transplant heads from body to body!), but it is a handy way to keep the Made of Iron creatures from ignoring what ought to be fatal injuries. It's also quite effective against most demons, servitors, mecha (logically or otherwise)...
- In Vampire: The Masquerade and its successor Vampire: The Requiem slaying a vampire requires either extreme mutilation or fire. A stake through the heart merely puts them in a torpor until it is removed.
- In Middle-earth: Shadow of Mordor, unless a named enemy of yours is beheaded when you finish him off (and there's no way for you to do it deliberately), you can bet that he'll eventually be back.
- Averted in the sequel: there's a small chance that even decapitation won't work. Likely the work of Talion and Zog's constant fingers to death having an effect on Mordor itself.
- In Saints Row 2, the Boss empties their magazine thrice into Mr. Sunshine, but he just refuses to die. So they chop his head off with his machete and toss it into a meat processor, which seems to work.
- In Battleborn, the vampire-like Sustained don't get sick nor age and they heal rapidly from most wounds. They however can be killed through decapitation as revealed in some lore from a visit by Randy Varnell at the Battleborn Discord Server.