Remember Mr. Mittens, one of our neighbors' cat? He is still around and he still comes to our door whenever he wants to go in his house. The other morning he was on our porch again, hoping we would walk him him over to his house and let him in, something we don't do when his owners are home.
Marissa happened to be sitting by the kitchen window and looking outside. The 2 cats watched each other for a while. There was some growling. That's when I lowered the window to prevent anyone attempting to pass thru the screen. Luckily, cats haven't figured out how to tunnel across barriers a la electrons.