This makes me think of a parasite called toxoplasmosa gondii...most of us have it in us, but our immune system takes care of it so that we do not get sick. However, when found in rats...it was attracted to the smell of a cats pee, so basically runs towards cats and gets eaten up. Rats have been evolutionary developed to dislike cat pee to elongate the survival of the species but put in simple terms... toxoplasmosa gondii changes the rat brain to go for the piss. The bacteria does that because it can only breed inside a cats intestine. So in simple terms, the rat is programmed to get eaten because of the parasite. In my immunology class we went over this, and one kid brought up about zombies, and was talking about how rats and humans are genetically pretty close (hence all skin products/drugs are tested on rats) and the professor explained it would only take a parasite like the toxoplasmosa gondii except in a more evolved form to "chew" up the human brain and cause people to do weird crap...such as eating others haha.