At the end of the second season of The Walking Dead we got our first look at Machonne, an incredible character carried over from the comics. In tow, she had with her two walkers, their arms lopped off, their jaws torn away, and their teeth ripped out.
Merle said it best when he said said there was a kind of irony in that.
Michonne used these two walkers as a sort of slave labor. They were used as pack animals when she loaded her bags up on them and they served as protection by masking her scent as she travelled around. Culturally, for Americans, the idea of two black men in chains being used for labor is a pretty disturbing image. So the fact that they were being used by another black person created an interesting juxtaposition.
At one point Machonne makes it clear that they deserve what they got, and since the story in the comics and the story in the show are somewhat different we have to take her word for it. Still, there is something pitiful about two walkers bound and mutilated the way they were that makes us wonder who they were and how they ended up the way they did, and why they deserved their fate.