Which runner looks bigger?

Once you think you know the answer, move the runner on the left next to the runner on the right to check!

This is called the Ponzo Illusion. This illusion happens because of perspective.

The runner on the left and the runner on the right are the same size, but the runner on the right looks bigger. It's believed that our brain makes objects that are farther away look bigger, so when objects of the same size are placed at a distance, they appear larger.