What was the last major change of the pigs to make them indistinguishable from humans in Animal Farm?
Animal Farm's pigs had already made the transition to nearly complete human-like behavior. They slept in beds, ate human food, drank liquor and, in the end, they proudly began to strut upright on two legs. When Napoleon met with their human neighbor farmers in the final chapter, this time in friendship, they toasted one another and Mr. Pilkington commented about the pigs "having your lower animals to contend with... we have our lower classes." They all rose on two feet and "clinked their glasses." Napoleon then announced that "Animal Farm" would revert to the old human title, "Manor Farm," and they toasted one another again. In the end, an argument broke out between the pigs and humans over a game of cards--both Napoleon and Pilkington had played the same card--and it became "impossible to tell which was which."
The animals went up to the window to make a look one last time and when the pigs and humans returned to their game of cards, someone cheated. Both Pilkington and Napoleon laid down an Ace of the same kind. In this moment, we can assume an uproar hit the table and in the fight or argument, the faces of the pigs became indistinguishable going from man to pig and pig to man. What I find interesting about this last change is that it is not a behavior effort for appearances, it is a moral change and a change that leveled the playing field between the pigs and the men.