There's a sneaky panda hiding in plain sight in a crowd of unsuspecting snowmen. Can you spot it?

It's harder than it seems. Hungarian artist Dudolf posted this ultimate Where's Wally cartoon on Facebook last Wednesday—since then, it's been shared over 111,000 times. Thousands of people have taken on the challenge to find the panda. For some it took only a few seconds, for others, significantly longer than that.

And some found "a dragon, 2 slippers, a can of pop," but no panda.

Can you find the panda?

So, why is it so difficult to spot the panda?

The answer lies in how human vision works and the method by which the brain carries out a visual search task. Most of the time we are actually very efficient at detecting unusual features in an image—for example, a red dot in an ocean of black dots would instantly pop out. But the "pop out" effect only works when the difference is in only one property, such as color or shape or size.

In other instances—in which the unusual feature shares some similarities to the rest of the image—the pop out effect breaks down and the task becomes significantly harder.

Here, the panda is obviously not a snowman, but it has the same black and white color, and more or less the same shape. So now that you can't rely on brain mechanisms behind the pop out effect, you have to actively search the image for the panda. That means, you have to scan the image in a serial manner until you find it. Sadly, there's no way around it. And for those people who found the panda in only few seconds, chances are they were just lucky to first lay their eyes where the panda happens to be.

Now, how about this cat hiding among the flock of owls?