mice can chew through almost anything remember that and the only need the tiniest of holes to get it. You basement is probably where the mice are coming in through. And they will travel through walls or floor, ceiling wherever. Calab may very well have eaten the mouse. My grandmother had a cat that would eat them. My two girls haven't caught a mouse but my RB Mytsi was an avid mouser. She loved to caught and torture them to death but once they were dead she lost interest. Then we had to make sure we got it before RB Shadow, our akita did. He loved them. He would also hunt them and kill and eat them.