- "We never destroy life deliberately. That is not our way."
- ―A Rill explaining the race's philosophy
The Rills are a sapient non-humanoid species whose hideous appearance contrasts with a pacifist and altruistic philosophy.
They are bulky amphibian-like creatures with scaly skin, several tentacles (six of which terminate in hands) and huge eyes; and need heavy fog-like ammonia-gas atmosphere to survive. They have no vocal chords and communicate telepathically with each other, but are able to use technology to convert their thought-waves into sound and communicate with non-telepathic species through their robotic servants, nicknamed the Chumblies. Like most non-oxygen breathers, an oxygen atmosphere is lethal to the Rills.
The metabolism of the Rills is so slow that they appear almost like statues, with only their eyelids opening and closing occasionally, at slow speed. From the Rills' point of view, humanoids appear as restless creatures that move at high speed like frenetic insects. In the Rills' time scale, a year is analogous to a week, and their life spans are appropriately many times longer than most humanoids'. A five-hundred years old Rill is roughly equivalent to a ten years old Human, although by that point they do have much greater experience and maturity, even in relative terms.
- Doctor Who Season 3 - Galaxy 4 (1965)