Since the Awoken seem to be Humans that have mutated. Then it may be that the Fallen are actually mutated animals? They can make out sound words that are similar to human speech which animals developed in another fashion that made them growl, squeek or whatever. Some animals that would be present in Russia are wolves, bears or dogs that often had packs or "Houses" if you will. One house if actually named "House of Wolves". I don't know why they are against humans, maybe they are trying to claim Earth from humans as we had claimed it from them in modern times? Anyways just my theory, what do you guys have for theories of the Fallen?