India, June 21 -- If you're looking for a new brain teaser to test your observation skills, a post shared by the Facebook page Funny Mafia might be the perfect challenge. The optical puzzle, simple at first glance, asks viewers to answer a seemingly straightforward question: "How many 7s are there?"

(Also read: Brain teaser challenge: Can you identify the robber in this tricky riddle?)

But don't be fooled. The image features a large figure shaped like the number 7, constructed using rows of the capital letter "Z". Mixed within these Zs are a few actual number "7" characters, subtly placed to blend in with the overall figure.

What makes the puzzle especially tricky is the visual similarity between the letter "Z" and the number "7"-parti...