I'm currently babysitting my friend's dog Max for three weeks (read all about it here).
Tonight I was watching a DVD, and Max was dozing on the floor beside the couch. When the movie was over I left the DVD player on, and after a few minutes the screensaver started up. It's a little floating blue cube that bounces back and forth across the TV screen.
Max immediately leapt up and stood in front of the screen, following the cube's every movement. Apparently it was the most fascinating thing he's ever seen.
I turned the player off a second after I snapped this photo, because he looked like he was just about ready to lunge at the screen and try to catch the cube.