Thousands of years ago there were a billion humans living on planet earth, creating man-made structures and buildings, all while destroying wild life and their homes. But then they died out because of a disease, surprisingly only affecting humans. Pets have began eating the remains of their owners, whether they be elders or even children. It was all the same to them. Wild animals were now roaming free once again, and although they can't tear down the man-made buildings and start anew, they can inhabit them. And that's exactly what they did. Until the disease evolved and became a disease that could now be spread in animals, too. And all those pet dogs and cats? They died because they ate humans who had carried the diseases. And now animals are more than likely to stay away from the rotting corpses. Animals have began killing the infected off, leaving room for the strong, healthy animals. But what happens when you eat infected meat and didn't know? You're only an animal, after all.