I had a cat in college that would try to pounce on football referees when they were on screen. I tend to believe that it keyed in on the black and white stripes, and accompanying color rainbows caused by NTSC composite video. The one I have now is too laid back though.
The dogs occasionally will bark when they hear animals or people knocking on doors, ringing door bells etc associated with things happnening onscreen, but they don't go for the trees.
My tiny Sony CRT is visually unconvincing.