What are some examples from Animal Farm of perversion of language?

The manipulation, or as the question puts it, perversion of language is a major theme of Animal Farm (and, for that matter, George Orwell's other famous book 1984). In Animal Farm, the most blatant and skillful manipulation is by Squealer, the pig who serves as Napoleon's spokesman and "propaganda minister."  He manages to use language to persuade the animals that their memories of the past were false, particularly when it comes to Snowball. For example, he tells the animals that rather than being a hero of the Battle of the Cowshed, as many of them actually witnessed, Snowball had in fact been fighting on the side of Jones. The pigs are also continually altering the language of the original Seven Commadments. For example, when the pigs begin sleeping in beds, the animals notice that the commandment against this practice now read "No animal shall sleep in a bed with sheets." When they begin drinking alcohol, they add "to excess" to the commandment forbidding alcohol outright. What is so clever about this is the fact that the pigs have created an environment where truth is so fleeting, so contingent on what they say, that the animals do not believe their own eyes. When Squealer tells them that Snowball was, in fact, a traitor at the battle, only Boxer dissents, and he suffers consequences. When the commandments are altered, the animals faintly remember something different about them, but not usually enough to serious cast doubt upon the pigs. So a big part of the pigs' rise to power is their skill in manipulating language.