Orwell uses point of view in Animal Farm to create irony. Irony is a contrast or contradiction, such as between what a statement seems to say and what it really means--or between what characters expect to happen and what really happens. The story is told from the naive point of view of the lower animals, not from that of the clever pigs or an all-seeing narrator. Thus, when there's a crash one night and Squealer is found in the barn sprawled on the ground beside a broken ladder, a brush, and a pot of paint, it is "a strange incident which hardly anyone was able to understand." A few days later the animals find that the Fifth Commandment painted on the barn wall is not exactly as they remembered it; in fact there are, they can now see, two words at the end that "they had forgotten." No comment from the narrator.
This simple irony is sometimes charged with great intensity in Animal Farm. For example, when Boxer, who has literally worked himself to death for the Farm, is carted off in a van to the "hospital," and Benjamin reads out "Horse Slaughterer" on the side of the van (too late), we know--and for once at least some of the animals know--what has really happened: the sick horse has been sold for glue. No irony. But when Squealer gives his fake explanation about the vet who didn't have time to paint over the slaughterer's old sign, we are gravely informed that "The animals were enormously relieved to hear this." And two paragraphs later, at the end of the chapter, when there is a banquet--for the pigs--in Boxer's honor, we hear the sound of singing coming from the farmhouse, and the last sentence tells us that the word went round that from somewhere or other the pigs had acquired the money to buy themselves another case of whisky." Most of the animals don't make the connection between Boxer's being taken away and the pigs suddenly having more money--and the narrator doesn't seem to make the connection either. But Orwell makes sure we, the readers, don't miss it. The irony--the contrast between what the animals believe, what the narrator actually tells us, and what we know to be the truth--fills us with more anger than an open denunciation could have done.