The credibility of the sites being used.
This final chapter depicts the complete transformation (not only in name) from Animal Farm to Manor Farm. There will never be a "retirement home" for old animals (as evidenced by Clover), and the pigs come to resemble their human oppressors to the degree that "it was impossible to say which was which."
The completion of the second windmill marks not the rebirth of Snowball's utopian vision, but a further linking of the animals and humans: Used not for a dynamo but instead for milling corn (and thus making money), the windmill's symbolic meaning has (like everything else) been reversed and corrupted. Animal Farm is now inexorably tied to its human neighbors in terms of commerce and atmosphere.
