What is this creature??

This little furball with huge teeth and claws has been found in our recessed windows wells TWICE! Once a couple of weeks ago and the 2nd time was on Sunday. What the heck is it? It's obviously noctural as it doesn't see well in the day as apparent when it's attacking the shovel Lance is trying to dig it out of the window well with. It's definitely aggressive as it was trying to chase both Lance and I on Sunday. Lance deposited in the field across from our house so hopefully it will stay there or move on for the fall and winter. Uggs found it the first time as he was tweaking out in one of our spare bedrooms. I went to check it out and there he/she was. Teddy found it on Sunday and was in the window well with it trying to attack it but he was too chicken, THANK GOD! I ran out there to see what he was barking at (his attack bark is much different then his ~the neighbors got a new car~ bark.) and quickly got him out of the window well and away from our fanged friend.

So...what do you think it is??