In this simple experiment, you can make it seem as though the arrows on a piece of paper move in the wrong direction. This is all due to refraction - as light passes through the glass, its speed changes and it refracts, slightly changing directions. The light eventually meets at a focal point outside of the glass and changes directions, resulting in a flipped image. For a more in-depth explanation, visit physicscentral.com. (via)
Image credit: physicscentral.com