Napoleon undergoes a dramatic change in the middle chapters of Animal Farm. He begins to exhibit more human qualities, and his selfish and greedy nature reveals itself. He is willing to stop at nothing to take and maintain his power.
For instance, Napoleon turns against his friend Snowball, who is a threat to Napoleon's power. Napoleon convinces the others that Snowball is actually an enemy and even forces him off the farm with the aid of his vicious "hired guns," the dogs. But that's not enough for the pig who has sneakily made himself the leader. Although Snowball is not physically present on the farm, Napoleon is not satisfied to have his enemies free; he essentially places a hit on his former friend, promising to reward the one who kills Snowball. Napoleon has hit a new low in blaming Snowball for the windmill's destruction and then challenging the animals to become murderers. He seizes any opportunity to remove blame from his own head and place it on his scapegoat, Snowball. Thus, he is also cementing his own power by removing his enemy.
Napoleon exhibits more and more human qualities in these chapters, however evil these traits might be. He plays mind games in slightly altering the commandments that the animals follow. He simply tweaks the laws and then convinces the animals that the laws have always been that way. A word or two excuses Napoleon's actions. "No animal shall kill any other animal" becomes "No animal shall kill any other animal without cause." He can use this particular law to justify turning against Snowball. "No animal shall sleep in a bed" becomes "No animal shall sleep in a bed with sheets." Snowball can now excuse the human act of living in a house.
In addition, Napoleon begins to work and trade more and more with humans. The arrival of Mr. Whymper is shocking, as the pledge to keep the farm for the animals seems to be threatened by a human's presence. Finally, Napoleon runs the farm as a cruel human would. The animals suffer as they toil all day without the tools that would make their jobs easier. Their lives are no better now than they had been before the rebellion, since Napoleon proves to be as cruel and uncaring as Mr. Jones. Clearly, Napoleon is using everyone for his own gain.