We had a squirrel in our kitchen once. Back in grad school, where I shared a house with two other guys. Freaked my housemate who was doing dishes at the time right on out.
I just caught the tail end of the commotion, but I'd guess the idea of a loose squirrel going berzerk in a confined space may be where they got the idea of Alien, with that bloody squirrel shaped little monster breaking through that guy's chest and running loose on the spaceship.