The narrator is an uninvolved third person (or possibly third creature) who we know nothing about and never see, and who apparently has no feelings one way or another on the whole thing. He weaves in and out of the creatures' heads, cluing us into things like Clover's distress about the executions.
One thing to notice. The narrator spends a lot of time being aggressively neutral with the passive voice. Take this instance: "It was noticed that they were especially liable to break into "Four legs good, two legs bad" at crucial moments in Snowball's speeches" (5.8).
Uh, okay. But who's doing the noticing? The narrator? The animals?
Well, most likely the animals. But the cool thing about this technique is that the narrator gives us the animals' perspective, showing us that they notice things but don't really get it. They can't put it together. It's up to us—the readers and the Westerners—to figure it out.