math jokes 4 mathy folks
 live. laugh. learn.

Are the blue lines curved or straight?

Place your mouse on the image, and click. The green lines will disappear, and you might be surprised at what you see! (The green lines will return when you release the mouse.)

This is known as the Herring Illusion, named after psychologist Ewald Herring. Although the horizontal lines are straight, they appear to be bent because the lines in the background create perspective and the illusion of depth.