Fur-Balls (a designation suggested by Dr. Gilmer, for the lack of a proper name) are a species of small, spherical fur-covered creatures native to the planet Mars.
They move with extreme slowness and their metabolism is slow in order to conserve the little oxygen and water which its desert environment can provide. The fur allows it to be insulated from the chillness of Martian nights. Perhaps most impressive of all is the way these creatures communicate, emitting ultrasonic sounds in extremely high frequency: about thirty million vibrations per second. They are noted as intelligent creatures, although whether truly sapient or not is up to speculation.
- Madness from Mars, by Clifford D. Simak (1939)
- Flat Cat - A somewhat similar species, also from the planet Mars, in Robert Heinlein's The Rolling Stones.