How is Animal Farm unrealistic?

Even Orwell himself described Animal Farm as a "fairy story." It involves animals who formulate a revolutionary ideology and stage a rebellion in which they steal a farm. They then set up a society on the farm that is more or less based on "Animalism," an ideology loosely based on communism. A group of pigs write "commandments" that the animals are to live by, and they have political debates, sing songs, and formulate grand plans to build windmills and other extravagant works. Throughout the story, they talk, gesture to each other, and express fairly obviously human emotions. By the end of the story, the pigs have begun to dress as humans, to walk upright, and are scarcely distinguishable from human beings. They have become transformed physically just as the society of Animal Farm has become corrupted. None of these things, of course, are intended to be believable. Rather, Animal Farm is an allegory for the society that has arisen in the Soviet Union, intended to demonstrate how ideals can become corrupted by power. This aspect of the book, sadly, is all too realistic.