Optical illusions can make us see things that are not immediately obvious. In this intriguing image, the challenge is simple: how many human faces can you find hidden among the trees? Before you begin, set a timer for 20 seconds and see how many you can spot.

But what causes optical illusions? Even when we think our eyes are focused on one particular point, they constantly make quick, almost imperceptible movements from one area to another. Our eyes collect separate details, and the brain combines them into an image that appears meaningful.

However, the brain can sometimes be fooled by familiar patterns and past experiences. For example, when we look at clouds, we may recognize the shape of an animal, a face, or even a familiar object. What one person sees may be completely different from what another person notices.

Now it’s time for the real challenge! This is no ordinary picture of trees. The branches are intertwined in unusual ways, cleverly hiding several human faces within the image. Can you find them all before the 20 seconds are up? Look closely—you may be surprised by how many faces were hiding in plain sight!