Tick by Akiyoshi Kitaoka
This is an interesting motion illusion that Professor Akiyoshi Kitaoka created back in 2010. When you simply look at it, you’ll just notice a series of different-colored square outlines. But if you use your scroll bar and move the image up and down, something interesting happens. As the actual image moves, the square insert also appears to move in alternating directions.
(via Akiyoshi Kitaoka)