In Chapter 8 of Animal Farm by George Orwell, what does Boxer say when told the Battle of the Windmill was a victory?

At the Battle of the Windmill, Frederick's men, who have already cheated Napoleon in the purchase of timber, blow up the animals' newly completed windmill. In a frenzy of rage, the animals drive the humans off Animal Farm. Squealer calls this a victory, and Boxer responds by asking how this could be a victory when Frederick's men blew up the animals' windmill. He is told that the animals were victorious in driving the men off their land. Boxer, who is weary and has been shot with pellets in his hind leg, points out that means the animals merely won back what was already theirs. 

At this point, the faithful and solid Boxer sees through the propaganda the pigs are using to try to put the best possible spin on Napoleon's mishandling of foreign policy in trusting Frederick and the disaster that resulted from that misplaced trust. Boxer speaks truth to power in saying this battle was not much of a victory. We also note that this strong supporter of the rebellion and the cause of Animalism is beginning to weary and to understand the ideals of the rebellion are not playing out as planned. Boxer notes that he is not as young as he used to be and seems to understand rebuilding the windmill will not be as easy as Squealer says it will be. Boxer steals himself to the task, but some of his earlier enthusiasm is wearing off. This indicates that the earlier ideals of the rebellion are being replaced more by a dogged sticking-with-the-program, but at the cost of less enthusiasm and hope from once-animated true believers like Boxer.