These large, almost cat-sized rats are common to many urban areas, especially those where the poor live. They are usually colored dull gray to brown, with peculiar, almost camouflage, patterning to their pelts. They are tremendously hardy, and, through a quirk of evolution, they don't carry diseases to humans- any disease that could infect a human is either neutralized by the rats' immune systems, or kills the rat quickly. They are widely regarded as good luck animals, thought to be very gentle and mild (even though they aren't), and are thus called "mice" as opposed to the rats they are. In truth, they're the result of a Second Republic genetic engineering project to drive disease out of low-income or newly-colonized areas by introducing them to push out the rat population. As such, they are quite prone to mutation. These mutations are usually of the typical, crippling kind, but there is a relatively high incidence of "superbright" Welland Mice with about the intelligence of a dog. These are highly prized and seen as especially good luck.