India, Aug. 27 -- Optical illusions are a fascinating way to pass the time. A new challenge that is grabbing attention asks players to spot the odd number. If you think you have exceptional eyesight and great observation skills, then this puzzle will intrigue you.

Optical illusions often force us to look beyond the obvious and play tricks with our brains. This viral challenge features multiple columns of the number '27'. But hidden somewhere in this picture is the odd number '21'. The only task that players have in hand is to spot the odd number in this image.

The real challenge is that players only have five seconds to solve this brain teaser. Experts believe that playing such games regularly can be a healthy exercise for our visual sy...