My theory is we are supposed to kill the mice. There are not enough animals, and many times no animals, to thin the herd and if we don't natural selection them, it will imbalance nature. We will have too many at the rate they multiply. My mother always said for every one mouse you see, there are at least 100 hiding in your walls. When she would say this my dad would contradict her and tell her that is the number if you have a cat. 200 Plus without. Now that freaks me.