A few days ago, a photo went viral on social media with people saying they could see a moody image of a beach instead of what the image actually was: a photo of a broken car door.

The optical illusion went viral because people were baffled by how easy it was to see something that wasn't actually there.

A neurobiologist has now explained how this type of optical illusion works. Bevil Conway told Time magazine it is all related to the way the light hits your retina, which is called "sense data" and what people expect to see when they look at the image.

"Our brains rely on information about what you expect because the sense data are usually pretty noisy, even if your experience of vision seems vivid—sometimes the squiggle in your peripheral vision is a bungie cord, and sometimes it's a snake," Conway told the publication. "The context helps you figure that out."

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To further explain, Conway says that someone hiking in the Amazon jungle will register the peripheral squiggle as a snake while someone parked in their driveway will see it as a cord. It all depends on the context in that moment.

Because people are not used to see photographs of the bottom part of a car door, no one expects this photo to show that.

However, since it is summertime in the northern hemisphere and many people are on beach holidays, it is not far-fetched to assume this could be just another holiday snap.

"The result is a potent mix of expectation and sense data that tilts heavily, for some people, towards seeing a sparse beach scene," the neurobiologist said.