Once it starts running, it doesn't stop. Its tiny brain makes it so stupid that it can't remember why it started running in the first place.
Biology
Physiology
(Bulbapedia)
Rhyhorn is a rhinoceros-like creature with a body covered in gray, rocky plates. Its underside and rear are smooth, and it has four short legs with two claws on each foot. It has a triangular head with narrow, red eyes, two fangs protruding from its upper jaw, and small, triangular openings on the upper sides. A spiked ridge runs along its back, and it has a single short horn on the tip of its snout. The female has a shorter horn than the male. In addition to its rocky hide, its bones are a thousand times harder than human bones.
Natural Abilities
Rhyhorn's brain is very small, giving it a one-track mind. When it runs, it forgets why it started and continues until it falls asleep. However, it may recall the reason upon demolishing something. Rhyhorn runs in a straight line due to its short legs making it inept at turning. It does not care if obstacles get in the way, merely smashing through them or sending them flying. Sometimes it may feel pain the day after a collision.
(Bulbapedia)Its design appears to be inspired by an Indian rhinoceros, with similar plated armor, and an Uintatherium from whom it may have taken its flat head and horn, with elements of ceratopsids.
Name Origin
(Bulbapedia)Rhyhorn may be a combination of rhinoceros and horn. Rhy may also derive from the igneous rock called rhyolite, alluding to Rhyhorn's Ground/Rock type combination.