“Houyhnhnms” in Gulliver’s Travel is a--

In the extremely bitter fourth part, Gulliver visits the land of the Houyhnhnms, a race of intelligent horses who are cleaner and more rational, communal, and benevolent (they have, most tellingly, no words for deception or evil) than the brutish, filthy, greedy, and degenerate humanoid race called Yahoos, some of whom they have tamed—an ironic twist on the human-beast relationship. Source: britannica.com