Although George Orwell shows several themes in Animal Farm, one of the most important is that of propaganda and how it affects public perception. Throughout the book, the pigs use Squealer, a very intelligent pig, to push their agenda and keep the other animals from thinking about their roles:
"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!"
(Orwell, Animal Farm, george-orwell.org)
Here, Squealer appeals to both fear and emotion; the animals don't want Jones back, and Squealer says the pigs need extra food to keep that from happening, but if they are denied extra food, Jones will return. The animals can't seem to see past this circular logic, and so accept that the pigs require more than their fair share. Public perception of what is acceptable is deliberately altered and shaped by the positions put forth by the government (the pigs) and debate is first discouraged, and then outlawed. Orwell uses Squealer as a metaphor for government-run newspapers and radio, which push the accepted government agenda without bi-partisan opinion.