The poison (most likely arsenic) in the rat killer poisons the rat, therefore killing the rat because of the poison. The actual effect of most rat poisons on a rat is to cause the animal's body to...
There is no such thing as a "pack rat." It is a sterio type given to rats because of there burrowing nature. but roof rats and norways can mate.
Pack rats do, indeed, exist (see link) but they are...