The Butcher's Nails are a surgical procedure in the Warhammer 40K universe originating from the world Nuceria for its slave gladiators.
Being a particularly rough brain altering surgery, large amounts of nails trailed with cables are inserted into the skull to amplify their anger and rage. The primarch Angron had them forcefully inserted during his life as a slave gladiator in his youth. He would later demand his world eaters legion proceed with an imitation surgery.
The cables on the patients' heads either look like mechanical dreadlocks or finer cables depending on the maker.
