In Animal Farm, how does Orwell manage to describe Boxer's 'disappearance' to create sympathy, anger and sadness?
I think one of the most important ways that Orwell establishes massive reader sympathy for Boxer in his novel is by consistently portraying him as the hardest working member of the farm and highlighting his constant self-sacrifice that he makes on behalf of the farm and its various projects. For example, when Boxer collapses in Chapter 9, note how his first thoughts are of completing the windmill:
"It does not matter. I think you will be able to finish the windmill without me. There is a pretty good store of stone accumulated."
He out of all of the animals has been the most loyal (and therefore the most manipulated) to the farm project.
What also adds to the sympathy we feel for him is the addition of Boxer's plans for his retirement:
Boxer professed not to be sorry for what had happened. If he made a good recovery he might expect to live another three years, and he looked forward to the peaceful days that he would spend in the corner of the big pasture. It would be the first time that he had had leisure to study and improve his mind. He intended, he said, to devote the rest of his life to learning the remaining twenty-two letters of the alphabet.
By revealing Boxer's plans in such a way Orwell ensures our anger that he is robbed of the peaceful life he deserves after all of his toil, especially when we find out that Napoleon has sold him to be slaughtered.
Thus Orwell creates tremendous sympathy for us by describing Boxer's unstinting work and the way that he is exploited by Napoleon and denied his long-awaited retirement only to be callously disposed of.
Boxer, the great pillar of the workingman's strength and commitment, is ultimately betrayed by the pigs, the primary benefactors of his dedication and work ethic. Far worse than simply allowing him to retire, or even to die amongst his friends (though his wounds were surely not fatal), the pigs sell him “for parts” and use the proceeds to buy alcohol. The pigs then tell the other animals that boxer died praising the farm.
This scene shows the disparity between what should be and what is on the farm. In a just society, those who believe in the society and work for it should be cared for and supported out of respect for their commitment, especially if they sacrifice their health for it. Under the rule of the pigs, animals are worth only what they have to offer to the community. In Boxer's case, once he had worked himself into decrepitude, his value was diminished to the price that his body would fetch for glue and the propaganda that the pigs could build based upon his martyrdom.
We feel sympathy for Boxer because of the tremendous injustice done to him by his those who benefited from his labor (according to Dante, the lowest circle of Hell is reserved for those who betray their benefactors). We are sad because Boxer is one of the most likeable characters in the story. And finally, we are angered by Boxer's fate because people mostly believe in a fair and ordered universe in which good deeds are rewarded and evil deeds are punished. Instead, in Boxer's case, as in Snowball's, and, in fact, through the rest of the story, we are denied the moment of terrible retribution and justice that is well deserved by the pigs. We are denied the sight of Napoleon's head being paraded through the streets of Paris or Squealer being tried at Nuremberg. The bad guys win, and the world is poorer for it.