This one has been cropping up more and more.
When I first brought up Unknown #1, my wife explained that it was not her cat, she didn't know why it was hanging around, and that more than likely it belonged to someone and was just wandering a bit. This would be comforting if I hadn't heard it before (see day 6 and day 11 for current examples).
And yes, it eats the food that is placed outside.
Other interesting facts.