In Robert Heinlein's science fiction novel The Rolling Stones, flatcats are a species of emotional symbiotes native to Mars, with very adaptive metabolisms.

They are small, furry, omnivorous, non-predatory, flatish, purr, and make their potential predators sufficiently happy to tolerate their presence, and perhaps even to feed them. In the absence of food, they estivate (or hibernate) by becoming inactive and reducing their metabolism to extremely low levels. This is a survival mechanism that might very well be expected of a species from a resource poor and environmentally strenuous planet such as Mars. When food becomes more abundant, they reproduce rapidly to take advantage of the more favourable conditions.

Because of the latter, flatcats are widely believed to have been the inspiration for The Trouble with Tribbles, an episode of the original Star Trek television series, in which tribbles display similar characteristics. However, in David Gerrold's account of writing the episode, he states that this was not the case.