User blog comment:TheNewProtagonist/Let's talk about the Grimm/@comment-68.226.106.213-20131014040315/@comment-3146930-20131014094035

There are actually a few ways they could multiply. The problem with the idea of the Grimm infecting other animals is that there are so many different types of animals, it doesn't make sense that there would only be 4 types of Grimm (so far). Not to mention that most Grimm are like cookie-cutter monsters, possibly meaning that the Grimm are manufactured by some kind of intelligent design.