Symbolism, Imagery, Allegory
When they first leave town, Edmund sees a little dog that runs to keep up with them. He thinks to himself: "The dog was too small to guard a hall, too big to hunt mice. Who was I to tell the little dog he was making a mistake?" (9.23). Sound like someone you know? Yeah, it reminds us of Edmund, too.
Unlike Edmund, who's helped by Nigel, the dog is left to fend for himself. That's a bummer for the pup, because soon two bigger dogs come along and tear the little guy to shreds. Since this incident comes shortly after Otto's hand is cut off, it has a deep impact on Edmund, who has nightmares that night:
When I closed my eyes I saw my master's hand, spiked to the anvil. I saw the startled eyes of our dog companion, and the spreading blood of the suddenly headless mastiff. (9.38)
If you've read up on Otto's hand elsewhere in this section (you totally should if you haven't), then you know that the severed hand represents Edmund in some ways. And guess what? So does this helpless pup. Without Nigel taking him under his wing, Edmund really doesn't stand a chance—just like the little dog doesn't survive when Edmund doesn't do anything to help it. As Edmund is haunted by both the hand and the dog in his sleep, we can see that he knows how dependent he is on others in order to survive, and just how violent his own end could be.