The first acts of the pigs to set themselves apart as a privileged class occur in chapter 3. In this chapter, we learn that the pigs do no actual farm labor but supervise the work of the other animals. The pigs are also the only ones who put forth resolutions at the Sunday meetings, more evidence that they are dominating the leadership of the farm. They organize the committees and classes.
The pigs set up the harness room as their headquarters. More ominously, they take for themselves the milk and the windfall apples. There is no discussion of this beforehand, as might be expected if all the animals really are equal. The pigs simply decide to do this and then explain it after the fact. Squealer tells the other animals that the pigs need the extra food because of all the brainwork involved in running the farm.
A fact that is slipped into this chapter almost offhandedly is that Napoleon has taken puppies aside to raise privately. Again, his right to do this is never discussed or debated: he simply goes ahead and does it.
In chapter 4, Snowball studies military strategy and leads the animals to victory in the Battle of the Cowshed.
The other animals should be paying attention and stopping the pigs from allowing themselves extra privileges, but they don't realize the extent to which the pigs, especially Napoleon, are quietly seizing power.