A Spy-killer was a device about the size of a baby's fingernail that was embedded into a being's skull that contained a small amount of explosives. Unless activated, the embed unit would otherwise sit harmlessly in the victim's skull. However, it could be set to activate if a particular word was spoke by the victim, thus ensuring that they would never be able to talk under interrogation.

Celot Ratua Dil used a disabled Spy-killer to convince Brun into helping him escape Despayre.