You are familiar with the rotating snake illusion. (You can test yourself here) As your eyes move over the image, they appear to move. But if you hold your gaze still in one spot, the movement stops. Now try explaining that to your cat!
Ryan Kotzin printed the illusion out and gave it to his cat Peter. The cat saw the movement and was as mesmerized as any human. After not getting anywhere with the moving snakes, he ate them.