Why Do Shapes Appear to Move When You Scroll?

Imagine you're looking at a grid of squares on a piece of paper, and you move the paper up or down slowly. The squares don’t seem to move, they just shift position. But if you look at them while scrolling on your phone or computer, the shapes seem to be moving! This happens because your eyes are used to seeing things stay still when you move your head or body around. When the screen moves, it tricks your brain into thinking the shapes themselves are moving, like they're dancing in place!