India, Aug. 30 -- Optical illusions are images or designs that trick our eyes and brain. They make us see things that are not really there, or see movement where nothing is moving. These illusions happen because our brain tries to make sense of patterns, colours, and shapes.

Such illusions are more than just fun pictures. Optical illusions show us how the brain and eyes work together.

Here's one such optical illusion shared by @factlio_ on Instagram that challenges you to test your observation skills.

In the middle of an eye-catching design is a square. At first glance, it seems to move on the screen. Your eyes feel like it is shifting from one side to another. But in reality, the square is completely still.

Only people with sharp eye...