The Swarm worked like a disease, spreading through electrical pulses which needed to make contact with a victim's eyes. This would turn victims into agents of the Swarm, answering to a Nucleus, a microscopic and virus-like sentient organism that controlled the swarm. Visually, an infected lifeform could be recognised by the growing of grey filaments around their eyes and hands. There was no physical matter for the virus, which existed in the mind-brain interface. The Swarm could affect non-living sentients such as robots. (TV: The Invisible Enemy)