Houyhnhnm means horse convey idea of perfection of nature .they are morally so good that there is no word in their language for lie or false hood friendship and benevolence are their two cardinal virtues not human
Yahoo are the brabic rays who where greed for food and collecting of shinning stones. They always fight for food when they also had sufficient food for them. They are the only animals which fall sick in the land of Houyhnhnm.
      Houyhnhums are very innocent creatures  which do not lie. They only speak truth they live close to the nature they use only yahoos for evil