In "The Abominable Snowmen" the control spheres are depicted as capable of seeking out inactive Yeti and crawling into the robots to activate them, emitting a series of whistle-like beeps whilst doing so. If the cavity intended to house the sphere is blocked, as Jamie (Frazer Hines) does with a rock, the sphere ignores that Yeti and falls silent. "The Web of Fear" expanded upon the spheres as a plot device with Professor Edward Travers and, as the serial progresses, the Doctor experimenting upon them. The experiments of both Travers and the Doctor eventually allow the protagonists to control the sphere, and by extension any Yeti it is stored within, using a short-range remote control.