The Bird
We've already discussed the poor little bird in the "Vanishing Cabinet" section, but we say he's earned a special shout-out because he's so much more than a pawn in Draco's little repair project.
Sure, the bird is primarily a demonstration of how Draco can send/receive stuff from a very not-nice-person. Draco sends the live bird somewhere through the cabinet, and it comes back dead. The meaning, as we've discussed elsewhere, is pretty clear: the cabinet can bring evil into Hogwarts. Shudder.
However, that bird clues us into some happier/more positive stuff as well. First of all, Draco cries when the bird comes back dead. No, no, we're not saying that we like seeing Draco cry…eh, well, actually, maybe we are.
See, it's proof that Draco isn't totally evil to the core. He's really riding the struggle bus with his mission from Lord Voldemort, and clearly doesn't like seeing an animal die. The ill-fated bird gives us a glimpse of humanity in Draco that we might not have seen otherwise.
Oh, yeah, and going back to that "ill-fated" thing: the bird actually shows up alive later, when Harry and Ginny are in the room of requirement to hide the Half-Blood Prince's book. Well, we think it's the same bird. What else could it be? How many birds can be floating around that vanishing cabinet?
Anyway, things are getting pretty lovey-dovey between Harry and Ginny on their little mission, and when they open the cabinet and the live bird flies out, it kinda feels like a symbol of how love and friendship can revitalize…well, anything. Even a dead bird, apparently.
So, yeah, there's lots going on with the bird, symbolically speaking.