On Nuceria, “butcher’s nails” was arena slang long before it was hardware. It meant fighting with nothing but your hands, stiffened fingers driven into eyes and throats, the cheapest way to kill a man when the pit masters hadn’t bothered arming you. Then the same phrase got bolted onto the thing they hammered into the back of a gladiator’s skull, and now it’s the title of a Hammer & Bolter episode.
Which was meant to be out this month, and isn’t. GW pushed The Butcher’s Nails back to October on the 14th, explaining that the animation team “needed a few more weeks to apply extra coats of Blood for the Blood God to really do it justice.” I genuinely can’t tell whether that’s a joke about render times or a real note from a producer, and I’ve decided I’d rather not find out. There’s a clip out as an apology.
The episode follows a World Eaters Berzerker called Makrath into an assault on an Imperial-held bastion, with the XII and the Iron Warriors working the same objective against Imperial Fists and Astra Militarum. Fourteen minutes, and per GW’s own description it’s almost one unbroken fight scene. The detail that got me was the camera. Much of it is shot from inside Makrath’s helmet, so a big chunk of those fourteen minutes is just what a Berzerker sees through his own eye lenses while he works.
What the Butcher’s Nails actually do
For about a year I went around my local store describing the Nails as a rage amplifier. Aggression dial goes up, warrior fights harder, everyone in a five metre radius dies. That’s the version in every summary box, it’s the version I repeated with total confidence, and Kiran let me do it for months before mentioning he’d read the actual passage.
The mechanism is subtraction. When the Nails activate they suppress serotonin production and deaden electrical activity across the brain, leaving only the adrenaline pathways running clear. Everything outside rage gets dulled to nothing or rewired into pain, so the bearer can experience pleasure during acts of violence and at no other time. Think of a phone where somebody’s gone in and deleted every app off the drive except one. You’ll be using that app.
The examination is the part I keep coming back to. After the Emperor pulled Angron off Nuceria, the archmagos veneratus of the Legion, Vel-Kheredar, spent seven solar hours going over the implants while Malcador kept the primarch unconscious and watched him work. What he found was that the Nucerian surgeons had cut out Angron’s limbic lobe and insular cortex before they put the device in. The Nails weren’t sitting on top of damaged tissue. They were doing that tissue’s job, badly, and had been for years.
That’s also why nobody could take them out. The tendrils had threaded down through the central nervous system and coiled around the spinal column, and the sections handling emotional regulation were the only thing keeping him upright. Vel-Kheredar wrote it all up, worked out that the device would eventually kill its host, and got back a sealed scroll with the Palatine Aquila on it telling him to bury the findings and never speak of them. The Legion was already the last to find its primarch and already had the worst morale in the Crusade. Telling them their father was on a clock would have finished it.
There’s a version of the Emperor’s decision here that’s straightforwardly pragmatic. A compromised primarch is still a primarch, he can still lead armies, put him back to work. I’ve read that passage half a dozen times and it lands differently every time depending on what mood I’m in.
Worth getting straight, because I had this wrong too: the implants in the rank and file are a different device from the one in Angron’s head. The Legion’s are primitive copies, and they stop short of the terminal degeneration his carried, so an ordinary World Eater has no countdown running on him. They match the original on the part that counts. Pull one out and the host dies, and on a good day he only ends up with brain damage nobody can repair.
The Cruciamen
The bit I only learned recently is that the Nails aren’t Nucerian in origin at all. They’re Dark Age archeotech, and in the profane texts sealed inside the Hexarchion Vaults on Mars they’ve got a different name: the Cruciamen.
The Emperor eventually brought Arkhan Land to Terra for a second opinion, sequestered him in a secret laboratory built inside a dead volcano, and had him look at Angron while the primarch lay unconscious. Land knew the name. He’d seen it during his expedition into the Hexarchion Vaults, in among the material the Emperor later had resealed by decree because it constituted knowledge that could pervert human cognition. He’d never seen one implanted and running. And the versions in the vault on Mars were cruder than the Nucerian build.
Sit with that for a second. Some backwater slaver aristocracy on the edge of Segmentum Ultima had a better-engineered version of a device that Mars kept behind a sealed door as a moral hazard, and they were using it to make their gladiator fights more entertaining.
The other Butcher’s Nails
GW has used this title before. Butcher’s Nails is a Horus Heresy audio drama by Aaron Dembski-Bowden from 2012, Angron and Lorgar on a joint operation, and it was the first Heresy audio Black Library gave a fully voiced cast. It runs about an hour. It opens with Angron working out whether to blow the Word Bearers fleet apart with Lorgar still aboard it.
I’ll be honest, I think it’s thin as a story. It’s there to set up Betrayer, the Eldar show up to inform Angron he’s fated to become the Blood God’s son in case anyone in the audience hadn’t worked that out, and then it ends. What it does have is a moment where Lorgar looks at the hardware in the back of the legionaries’ skulls and realises the implants have been walking the XII toward Chaos the whole time, independent of anything Horus ever said to anyone. Then at the end he tells Angron he was mistaken and there’s nothing wrong with the Nails, which flatly contradicts the scene, and I’ve never seen anyone explain it.
Whether the animation adapts any of that or just borrows a good title, GW hasn’t said.
The Legion queued up for it
Angron didn’t invent the World Eaters’ version. He ordered his Apothecarion to build one, using his own implants as the template, which was awkward because removing them for study would have killed him. The early attempts went about how you’d expect: high mortality on the test recruits, and among the survivors an irrecoverable homicidal frenzy. It took a Master of Inductii named Gahlan Surlak to get a workable pattern, and even then it never produced consistent results between subjects.
After the Ghenna Massacre, whole newly-formed companies went under the knife at once, alongside a lot of existing legionaries who volunteered. Most went back into line units. The ones judged too unstable got shunted into Rampager squads, and the ones beyond even that became the Caedere, the Butchers, who had to be physically restrained between battles.
So yeah. They asked for it. That’s the part that gets skipped when people talk about the XII as victims of their gene-father, and it’s the reason Endryd Haar declining the implants is such a strange, load-bearing detail. Angron gave the order, sure. But he could not have physically compelled a hundred thousand transhumans to open their own skulls if they’d said no. They said yes because their father was visibly broken and they wanted to be broken the same way, on the theory that shared damage counts as kinship. Which they got, I suppose.
Although. I keep saying “chose,” and I’m not sure how much choosing is left in a Legion where the primarch has done it, the veterans have done it, and next month’s intake will be doing it as standard procedure. That’s a queue you’re already standing in by the time anyone asks. The Emperor censured the Legion for the psycho-surgery they were running on new recruits, which puts the end of anything voluntary well before Isstvan.
I bought the Khorne Berzerkers box in 2023 off the back of exactly this lore, on a Saturday, in a shop, having gone in for a pot of Kantor Blue. My Thousand Sons were half-finished at the time and remain so. My unbuilt boys are still shrink-wrapped in the bottom of the cupboard under the Leviathan sprues, and every time Kiran comes over he does the bit where he asks how my World Eaters are coming along. Three years of that. I’ve had roughly ten years in this hobby and I’ve completely changed my mind about two armies in that time, so the Berzerkers still have a shot…
The Librarians
The XII had psykers. A whole Librarius, aboard the Conqueror, right up until the Nails went in.
They got implanted the same as everyone else, near enough the entire Librarius inside a single month. One of them, attached to the 100th Company, lost control in his first battle post-implantation and burned three squads of his own brothers to ash because he couldn’t stop projecting lightning from his eyes. Others simply combusted. In a few cases a dying codicier pushed pain out through the implants of nearby World Eaters and dropped entire squads with strokes and brain haemorrhages at his feet.
They tried to master it. Told each other it was a question of willpower, and their battle-brothers pretended not to see how frightened they looked while they said so. They kept dying anyway.
Angron gave the survivors a choice between execution and having the Nails taken out. Every World Eater on that ship already knew removal was fatal, because the Emperor’s own techno-mages had failed to do it to the primarch. Most of them volunteered for the surgery anyway. It killed all of them, and with rewired brains misfiring on the table, it took a while in most cases.
Compare that to the Thousand Sons, who ended up unable to produce anything except sorcerers. The XII went the other way inside about a month of theatre time, and the halls of that Librarius stayed near-empty afterwards, staffed by the handful who’d never been implanted. Meanwhile the Berzerker-surgeons who inherited the work from those first Apothecaries have had ten thousand years to keep going, folding in daemonic pacts and warp-craft, deliberately making the device worse than the thing Vel-Kheredar examined in seven hours. Roghrax Bloodhand’s warband is out on the Eastern Fringe using the current build to collect Tyranid skulls, bio-titan craniums included. That’s the version of the device Makrath will be wearing in October.
