New Delhi, Aug. 12 -- A fresh optical illusion is making the rounds on social media, and it is testing just how sharp your eyes really are. The puzzle looks simple. A 16-by-9 grid is filled with repeating "2Z2" patterns. Somewhere inside that grid, one set is different. An odd "222" is hiding in plain sight.

Sounds easy? Most people think so until they stare at the screen for far too long without spotting anything. The answer is not random. But before you scroll down for the solution, try finding it yourself. The whole point is to see if your brain catches the pattern break.

At first glance, "2Z2" and "222" do not seem that different. That is the trap. Your brain groups the shapes together, especially because the letter Z and the number...