George Orwell's 1945 novella Animal Farm is an allegory in which the animals of Manor Farm overthrow their human owners and take over operation of the farm. They formulate a philosophy which comes to be known as Animalism. One of the man tenets of this philosophy is that animals are good, but human beings are bad.
As time passes, though, the animals begin to realize that their farm cannot produce everything the animals need to sustain themselves. To remedy this situation, the pigs, who hold the position of leadership on the farm, decide that they will need to start trading with other farms to make up for their farm's deficiences. Unfortunately, this means trading with human beings, who, according to the ideals of Animalism, are evil.
Gradually, this trade with the humans further corrupts the original ideals of the animals' revolution. By the conclusion of the novella, the pigs are walking on two legs, drinking alcohol, and playing cards with the humans. Thus, Orwell ends his novella with the chilling comment:
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.