The Doctor deduced they were blind because they seemed to feel their way around the exterior of the TARDIS. Later, he determined they had the ability to detect sound waves and heat. They were powered by a form of magnetism and could be immobilised by ensnaring them in a metal mesh. They resisted gunfire by voluntary deactivation. When they switched themselves off, their bodies telescoped down, reducing their height by roughly half. The concentric rings of metal that comprised their bodies folded into each other, thereby protecting the interior of the robot.