In chapter 6, Napoleon starts behaving in a number of ways that suggest he's betraying both the spirit and the letter of the Animalist revolution. He's begun trading with the hated enemy, humans from neighboring farms and businesses. Also, he and the rest of the pigs move into the farmhouse and begin sleeping on beds, a clear violation of the fourth of the Seven Commandments of Animalism. And when the rickety old windmill collapses, the fruit of all that sweat and labor by the animals, he shamelessly blames it on Snowball, who unlike him was a real hero of the revolution.
For the most part, the animals remain loyal, though there are one or two murmurs of discontent at recent developments. Squealer is pressed into service by Napoleon to sell the new changes to the animals, to convince them that they're entirely in keeping with the principles of the revolution. To that end, he goes round the farm assuring the animals that there was never any prohibition against engaging in trade or using money. If they think otherwise, then not only are they mistaken; they must have been dreaming.
Through the medium of propaganda, Squealer is trying to get the animals to subscribe to the alternate reality, the bizarre parallel universe that Napoleon has constructed. In making the animals doubt themselves, Squealer wants them to place their trust not in the truth of their own memories but in Napoleon. That way, it is hoped, they will become more loyal to Napoleon, strengthening his dictatorial power.