Puzzles can be a great way to sharpen your brain. But puzzles can be uncomfortable, especially when the answers elude everyone. Just think of Mona Lisa, displayed at the Louvre Museum in Paris. For 500 years the face on Leonardo da Vinci’s famous portrait has been debated to pieces: “Is she smiling back at me? Or not? Why? Why not? What is she thinking? Who is she?" Still the puzzles continue. Exactly like that there are questions around the whole issue of malnutrition, that seem puzzling—sometimes because they defy common sense, sometimes because the science behind them is too wacky and sometimes because the answers are so predictable that you find it hard to believe that they can still remain unsolved. So here are ten issues that—big and small—that, we believe, you need to read. Do let us know if you can crack them.