There is irony in the congratulations of the animals at the "Battle of the Windmill" for a couple of reasons. The first is that the windmill is totally destroyed. The congratulations of a battle would be in recognition of victory. The windmill was not saved, as it was obliterated. Yet, Squealer understands very acutely the nature of the animals. He understands that if all of the animals coalesce and share anger amongst one another, they can mobilize to get rid of the pigs' leadership much like all of the animals unified to get rid of Jones and the humans. In an attempt to misdirect them and placate them, Squealer declares success in turning back the humans and creates the "Battle of the Windmill" label and extends the congratulations. In doing so, the animals' attention is turned against the humans and not against the pigs' leadership, whose attempts to try to negotiate with both sets of human farms ended up causing the destruction in the first place. It is also ironic that congratulations was extended because of what follows it. The pigs' use "The Battle of the Windmill" as a way to get the animals to rebuild the windmill. In this light, the congratulations is empty. It is a pat on the back, followed by a whipping to get working on building it again.