Impressed by the virtues of the Houyhnhnms, Gulliver decides to tell, freely and truthfully, as much as he can about Man. Gulliver has come to venerate the Houyhnhnms and hopes to be able to stay among them for the rest of his life. But Gulliver cannot be absolutely truthful; he extenuates people's faults and over praises their virtues. The more Gulliver tells, however, the more thoroughly he convinces his master that there are genetic and psychological links between humans and Yahoos.
Swift sets up a point-by-point comparison between the Houyhnhnms' Yahoos and the European Yahoos he described earlier. He makes the moral flaws of Europeans vivid, concrete, and personal in the Yahoos. Yahoos collect stones as Europeans collect money. Yahoos fight among themselves like Europeans; their motive, like the Europeans' motive, is greed. They even have tribal politicians. The Yahoos get drunk and "howl and grin, and chatter, and reel, and tumble, and then fall asleep in the dirt." They are subject to melancholy and the "spleen" — fashionable complaints of rich Englishmen. For all their faults, however, the Houyhnhnms' Yahoos are not as vicious as the European Yahoos. What flaws the Yahoos have by nature, the Europeans increase and intensify through a perversion of their reason.
sordid animal a dirty, filthy, squalid animal; here, meaning a Yahoo.
by rapine or stealth rapine: the act of seizing and carrying off by force others' property.
malicious insinuation an indirect and, in this case, spiteful suggestion or implication.