Most of the fantastical locations in Gulliver's Travels are inhabited by beings who, despite differences in size and culture, are easily recognizable as human beings. The one exception is the land of the Houyhnhnms, which is inhabited by intelligent horses. Jonathan Swift uses anthropomorphism to attribute human characteristics, emotions, and behaviors to the Houyhnhnms, who act like humans in many ways. In fact, when Gulliver first encounters them in Book 4, Chapter 1, his limited perspective leads him to assume that they must be humans who have been magically transformed into horses:
[T]he Behavior of these Animals was so orderly and rational, so acute and judicious, that I at last concluded, they must needs be Magicians, who had thus metamorphosed themselves upon some design.
Many aspects of Houyhnhnm society are familiar to Gulliver. These anthropomorphized horses live in houses, cook their food, and have their own language and customs. But the Houyhnhnms also differ from humans in several important ways—being naturally protected from the elements, they have no need for clothes or shoes, and their society is free of human vices like dishonesty and greed. These horses don't merely act like humans, they are also superior to humans.
In order to emphasize this point, Swift contrasts these anthropomorphized horses with the uncivilized Yahoos, who are physically human but behave more like animals. In doing so, Swift challenges the European notion that humans are inherently the most superior species and argues that this supposed superiority is a result of culture rather than nature. As Gulliver spends more time among the Houyhnhnms and Yahoos, his own perspective begins to change, and he comes to view Houyhnhnm society as superior to that of his native England.