The fact that George Orwell refers to Animal Farm as a "fairy story" already prepares the reader for what they might read. The reader expects exaggeration and certainly a story with embellishments and vivid character representations. He uses anthropomorphism to emphasize his point as animals take on human characteristics and history repeats itself when power is exposed as an over-riding force allowing for exploitation, regardless of who or what is driving it. The very fact that "some animals are more equal than others," alludes to what will be a less-than-successful rebellion, although those in power would, ironically, disagree as Napoleon is very proud of his ability to walk on two legs at the end and the mantra becomes, "four legs good, two legs better."
Making use of animals as his main characters also allows Orwell, cleverly, to simplify his version of The Russian Revolution allowing the reader to step away from casting immediate judgment and allowing the subversion to, hopefully have an even bigger impact on the reader. Orwell also, presumably, reaches more readers as he is not restricted by those interested in the historical aspects of the clashes between Trotsky, Lenin and Stalin and can expose younger readers and those who would otherwise avoid the potentially, challenging nature of such proceedings to the damaging effects of the abuse of power. The style and tone which Orwell uses ensures that readers are able to draw their own conclusions, not only from the Marxist ideals of equality and the unfortunate reality of rules and "Commandments" which are subject to change but also from any form of control, about which Orwell himself became so disillusioned.
Orwell uses Old Major's speech in chapter one to cast doubt on the revolution. In his speech Old Major talks about how the idea of a revolution has been around for many years and will be around for many more. He tells the animals not to hope for it in their life times, but to work toward it for future generations so that perhaps they can revolt and overthrow man. The tone (speaking directly to a literary device or technique) of Old Major's speech about revolution has the sound of something happening in the distant future, certainly not within the lifetimes of these animals or even within that same year. Old Major makes it sound as if the revolution will be a long and arduous process that will take generations upon generations to achieve. He speaks about the work that has been done throughout past generations (Beasts of England is an old song he learned from his mother in their day). The reader is caught somewhat by surprise that the revolution takes place so suddenly and quickly in Chapter Two after his speech.