New Delhi, Sept. 20 -- Think your eyes are sharp enough to spot what most people miss? Here is the test. A viral brain teaser making the rounds on social media is pushing people to find one single number buried in a sea of identical digits. The setup looks simple: a full grid covered with 7s. Somewhere inside, a lone 1 is hiding in plain sight. The challenge-spot it in ten seconds or less.

On paper, it feels like a breeze. In practice, not so much. Staring at row after row of the same digit plays tricks on your vision. The brain tends to blur repeating patterns, which makes that one odd figure nearly invisible. That's the catch-and the reason people keep sharing these puzzles. They are quick, and once you solve them, it is very satisfyin...