TQC help! I've got two cats, a male and female. They've been living mostly peacefully (besides small playful scuffles) together since February. About ten minutes ago a stray (or stranger cat, he may have a home) showed up on our porch (we had windows open). Stray kitty and our kitties smelled each-other through the screen. Suddenly our kitties started freaking out and started attacking the screen and then each-other. We've got them separated right now, but there was angry growling and hissing and attacking of one-another. We've closed the windows and the blinds. Any notion what's going on or suggestions to make things better?