Mouse Theory

So I was heading down to my basement to store a chest, when I saw a mouse run along the corner of the floor. My first instinic was to throw the chest at the mouse but my better judgement intervened. So I just watched it crawl up the wall and then through the wall. I looked at the hole that he scampered through and realized that it led right into the storage space in the back of the house. This got me thinking. Perhaps there are no mice that live in our house but rather they come and go from the outside as they please. This is an idea that I previously never considered. Shortly thereafter, I took the insulation foam and sealed off all the cracks under the wall. So this action did one of three things: 1) cut off the mice from using that enterance, or 2) blocked off the mice already in my house from leaving, or 3) nothing at all and my theory sucks. Regardless of what I accomplished, having these mice problems is proving to be quite a battle.