the thing to keep in mind is what sort of bugs/parasites could that thing have picked up. rabbits tend to be pretty communal, so they trade bugs lots. Rats to a large degree as well, and since they are omnivores like us, there is a higher risk of parasites that also infect humans. But you know what other omnivore we have eaten for a long time? Piggies. Same deal. cook it well, and no worries. I would put them at about the same level of risk as far as infection went. There are few animals I wouldn't worry much about, but those are limited to herbivores that are fairly solitary, and there are not that many of those. porcupine comes to mind, but not much else, and porcupine can be toxic (or at least pretty nasty) if its been living on certain trees. I suppose in an urban area there is a greater risk of rat being pretty toxic as well, but same goes for bunnies that have been living on manicured lawns. Some of that would be cumulative toxins like heavy metals, so a once off survival situation wouldn't be a big deal, but some things are pretty bad for you and could start to cause problems pretty quickly, not sure the half-life of most rat poisons, and I don't really want to find out...