India, Aug. 29 -- Optical illusion challenges have always been interesting as they show how easily our eyes and brains can be misguided. Such puzzles are not only fun but also test how observant and focused people are. The latest brain teaser going viral is a number puzzle that looks easy at first, but gets tricky when you look closer.

The image has rows and columns of 51s all lined up on a pink background. At first glance, you will feel that every single number is the same. But that is where the challenge begins.

The task is to scan through the rows of 51s and find the odd number. In the middle of the grid, a lone number 15 is camouflaged. As the numbers look similar, your brain will automatically read them as 51 even when the digits a...