This is a good question. The use of rhetoric is central in Animal Farm, because the pigs, especially Squealer, uses rhetoric to persuade the animals that they are better under the Napoleon. In other words, the rebellion was a good thing and a huge success.
Moreover, in many ways, the rhetoric of the pigs was successful, because the animals actually believed that their lives were better under Napoleon than under Jones.
From this perspective, the rhetoric of the pigs was powerful, because the situation of the animals was far worse. There was less food, more work, even on the weekends, and no one retired. And most of all, Boxer, the hardest worker, was lead to be slaughtered. Therefore, Orwell uses rhetoric to show what it can do and how powerful it is.
Here is an example of the words of Squealer. It is a long text, but let me put in bold print some of his uses of rhetoric.
‘Comrades!’ he cried. ‘You do not imagine, I hope, that we pigs are doing this in a spirit of selfishness and privilege? Many of us actually dislike milk and apples. I dislike them myself. Our sole object in taking these things is to preserve our health. Milk and apples (this has been proved by Science, comrades) contain substances absolutely necessary to the well-being of a pig. We pigs are brainworkers. The whole management and organisation of this farm depend on us. Day and night we are watching over your welfare. It is for your sake that we drink that milk and eat those apples. Do you know what would happen if we pigs failed in our duty? Jones would come back! Yes, Jones would come back! Surely, comrades,’ cried Squealer almost pleadingly, skipping from side to side and whisking his tail, ‘surely there is no one among you who wants to see Jones come back?’