What did George Orwell mean by the last paragraph of the book?
The setting for the last paragraph of Animal Farm is a game of cards at the table in the farmhouse. The animals are looking through the window and watching as the pigs, Napoleon and Squealer, are playing with the humans. An argument breaks out when Napoleon and Mr. Pilkington both attempt to play an ace of spades, and it quickly becomes heated. The animals watching from outside cannot tell the difference between the pigs and the humans. The point is that the corruption of the animals' revolution is now complete. The pigs have become as bad as the humans that they fought to overthrow. There is literally no difference between them:
Twelve voices were shouting in anger, and they were all alike. No question, now, what had happened to the faces of the pigs. The creatures outside looked from pig to man, and from man to pig, and from pig to man again; but already it was impossible to say which was which.