Brusspup is the master of optical illusions on YouTube. Many videos will show you how the brain is tricked in numerous ways.
In this case you can see how two sliding sheets will generate the illusion of movement. Much the same as with early cartoons where you saw a ton of still images on a drum and, when moved fast enough, you would see some movement.
You can also have those sliding images at home. To download and print them check the video description from here.