Symbolism, Imagery, Allegory
(Click the symbolism infographic to download.)
Normally, we love dogs. We're the kind of people who end up squealing on a semi-daily basis, "Oooh, cute dog!" Send us a corgi video, and you're sending us happiness.
But, Their Eyes Were Watching God makes us reconsider our whole pro-dog stance. (For all of 30 minutes, but still.)
Because the dog in this novel is a symbol of a hate so vicious that it stops at nothing to lash out at another living being, it's blind to who it hurts. For Hurston, the concept of hate is so frightening and so unnatural that not even a savage animal is enough to convey it; this creature must be twisted in some vital way. In this case, the dog is afflicted with rabies.
Be afraid. Be very afraid of dogs with rabies...especially when they're symbolic.