Swarms of Ratz
From the point of view of many, rats are pests to be killed at first sight. They eat our crops and soil our houses. On second thought, however, the destinies of rat and man seem linked. Both species are survivors. We accused rats of being responsible for the black plague, the zombie disease, but it seems they carry the burden in the same way we do. They are vulnerable and can be turned into zombies. We call these the Ratz.
Ratz are as numerous as their brethren, of course, but their fear of man has been replaced with a hunger for human flesh. For an unknown reason so far, they act like a giant pack. As soon as some of them find a fresh food source, all ratz in the vicinity gather for the feast. The more there are, the more frantic these critters become, and you know how agile and fast a rat can be!