This photograph captures a heartwarming moment between two southern rockhopper penguins, the perfect image for International Kissing Day. Why do we kiss? Well, dozens of cultures don't kiss on the lips at all. For those that do, theories range widely, from the chemical reactions in the brain, to ancient ancestral parents chewing food for their children, to simply smelling each other. Of course, no scientific explanation can capture the magic of a shared kiss. Perhaps that's why artists including Prince, Faith Hill, and Hall & Oates have all had chart-toppers about lip-locking; they have found a way to put an indescribable feeling into words.