In George Orwell's Animal Farm, even though the initial ideals of Animalism suggested that all animals are equal, as the novel progresses it becomes clear that differences between the animals do exist. Pigs and dogs, for example, are explicitly said to be the cleverest of the animals. The dogs also emerge as the "muscle" behind Napoleon's power and he eventually uses the canines to threaten and terrorize the other animals.
Some debate also occurred over whether rats should be considered among the comrades of the animals on the Jones farm (it was ultimately decided that they should be considered "comrades").
The tame raven Moses was also clever, like the pigs, and had some animals convinced of his heaven-like Sugarcandy Mountain.
Two cart-horses, Boxer and Clover, are loyal and obedient to the ideals and leadership of Animalism, whereas the horse Mollie is vain and interested only in avoiding work and adorning herself with pretty ribbons.
The sheep, hens, and ducks are considered some of "the stupider animals", which prevents them from memorizing the Seven Commandments. The sheep, however, are adherent to the Animalism movement and their constant repetition of the motto "Four legs good, two legs bad" proved useful to the pigs in power.
The hens, who later become upset because Napoleon enters a contract with the humans to sell their eggs, were among the first to rebel openly against Napoleon and for this some of them were killed.
Ultimately, even the line between animal and human becomes blurred as the pigs begin to interact with the humans. Thus, the novel ends:
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.