After doing away with Mr. Jones, the human owner of Manor Farm, the animals collectively establish Animal Farm with a foundation of equality among and between species, from duck to dog, from pony to pig.
A series of predictable slippages first waters down their enthusiasm, then dilutes their autonomy in work, and finally removes their agency—minimal to begin with—usurped by the self-appointed brain workers, the pigs. Having asserted themselves, the pigs represent the reemergence of hierarchy at the very dawn of the revolution against their evil human keeper who for them, has forced such a framework upon them.
The pigs further assert themselves, moving into Mr. Jones's farmhouse and dictating the unequal approach to running the farm. Naturally, infighting ensues: the brutish Comrade Napoleon ousts the feisty Snowball— inefficient debate, already stripped from the animal collective, is further purged even from the ruling ranks.
The animals' hope-filled anthem, Beasts of England is abolished by the emboldened tyrant Napoleon.
The Seven Commandments are discreetly altered by the chief propagandist, Squealer, at Napoleon's behest; new words are painted onto the barn-side. 'No animal shall sleep in a bed' becomes 'No animal shall sleep in a bed with sheets' when the pigs discover how comfortable mattresses and blankets are when compared with straw and dirt.'No animal shall drink alcohol' becomes 'No animal shall drink to excess' when the pigs discover the warmth of whiskey.
And even the most cornerstone 'Four legs good, two legs bad' degenerates to these two logically inconsistent phrases:
All animals are equal / Some animals are more equal than others
And by the end, having learned to walk on two legs—but far from only that—the pigs have become exactly that which they despised: a manifestation of the worst aspects of humans, without any of the good.
But at least they have their slogans.