At first glance, it's just a couple sharing a hug on a beach. On second glance, it's a four-legged humanoid with two heads. What's going on? This photo, most recently posted by Reddit user Blood_Reaper on May 24, has been viewed nearly 11.4 million times in the eight days since. Its way of bending reality has had people around the globe staring at their screens and scratching their tilted heads in confusion.
The internet is just the modern way to enjoy and share illusions; man was sharing them via cave drawings and carvings 15,000 years ago, suggests a 2010 article from National Geographic. The pieces describes a study of several similar cave drawings and carvings, which, depending on how you view them, depict either a mammoth or a bison. The study states that the prevalence of the dual image, particularly in three-dimensional carvings, indicates that it isn't a mistake -- that early man intended for the image to be recognizable as either one animal or the other, just like similar illusions of today.

Optical illusions are popular because it's fun to marvel at things we see, or don't see, or think we see. Take another look at the eye-twisting photograph of the hugging couple -- have you figured it out yet?

(Hint: Take a close look at clothing.)