A picture is worth a thousand words, but if there’s an unexpected twist hiding in the background, it might be worth two thousand. We’re all familiar with optical illusions, but usually they are created on purpose. It’s a rare occasion when an unsuspecting photo becomes an optical illusion after people look at it and start saying, “Wait a second…” While most of the photos here are funny based on what’s in the background or peeking out from a corner, some are just our eyes playing tricks on us. 

To learn more about how our eyes can fool us, we checked out this Vox article that explains how each of our realities are constructed by our own brains. “It’s really important to understand we’re not seeing reality,” neuroscientist Patrick Cavanagh, a research professor at Dartmouth College and a senior fellow at Glendon College, told Vox. “We’re seeing a story that’s being created for us.” He explained that typically, what our brains tell us does match up with the real world, but sometimes our brains work to fill in gaps, which can warp our perception of reality. 

In his article, Brian Resnick explains that the fact that visuals can trick us may seem disheartening at first, but we shouldn’t look at it that way. We can actually learn a great deal about how our brains work when we know what can confuse or fool them. He goes on to explain that the more we understand about how our brains work, the more we might be able to understand one another. Rather than being frustrated by someone who perceives the world differently, have some compassion. After all, their brain is feeding them a slightly different message than what yours is telling you. We should be curious about these differences and investigate them.

Brian also poses the question of why we are seeing a story of the world rather than the full picture. Apparently, we evolved to be this way. “We don’t have the necessary machinery, and we wouldn’t even want it, to process carefully all of the amount of information that we’re constantly bombarded with,” Susana Martinez-Conde, a neuroscientist and illusion researcher at SUNY Downstate Medical Center, told Vox.

When we see an object move, for example, there is a complicated process happening inside of us. “Once light hits the retinas at the back of our eyeballs, it’s converted into an electrical signal that then has to travel to the visual processing system at the back of our brains,” Brian explains. “From there, the signal travels forward through our brains, constructing what we see and creating our perception of it. This process just takes time.” 

If we only relied on what our brain had fully processed, our reflexes would be too slow for us to have very good coordination. So we need our brains to fill in the gaps and make predictions for us. When we see something moving, we see it just a tad bit further along than it actually is because we know where it’s headed. And when we see a confusing photo, it can be very hard to convince our brains that what it initially thought was happening might not actually be the case.

Adam Hantman, a neuroscientist at Howard Hughes Medical Institute's Janelia Research Campus, explains that we are almost always relying on predictions that our brain makes and then using our senses to course-correct any inaccurate predictions. Even the way we see colors can be confusing. Most of the time we can agree with others about what color something is, but sometimes colors are up for debate. Do you remember the infamous white and gold or blue and black dress? An interesting development from that whole dress drama was the theory that someone’s lifestyle might affect how they perceive images and colors.

In a study on the infamous dress conducted by Pascal Wallisch, he found a strange correlation between those who agreed on the color of the dress. People who consider themselves night owls were more likely to see the dress as blue and black, while early risers, or larks, were more likely to call the dress white and gold.     

Wallisch believed that the reason for this correlation was because participants assumed the lighting on the dress was whatever they are more familiar with. For example, larks spend more time experiencing natural light than night owls do, so if they view the image like it is being drenched in sunlight, it appears white and gold. On the other hand, night owls tend to assume that there is fluorescent light on the dress, which would make it appear blue and black.

“The owls versus lark data seems quite compelling for explaining a large part of the individual differences,” says Sam Schwarzkopf, a vision scientist at the University of Auckland. But it does not explain everything. “There are still lots of other factors that must have a strong influence here. It could be prior experience with the subject matter, or related to other aspects of people’s personality,” he says. “Yes, the dress continues to mystify.”

Our brains have all sorts of biases, and they are used to ignoring information that does not serve us or overloads us. We filter out things like the fact that we can always see our noses because it does not serve us. We don’t need to see our nose; we know, or should I say knows, it’s there. But a similar thing happens when we see an image where there is just too much going on. We can’t necessarily see every detail, at least not at first glance. So that’s why it might take you a moment to catch a cat hiding in a pillowcase or a child in the corner in these photos. We can only handle so much information at once, and if there is something you’re not expecting to see, your brain might just ignore it.  

When it comes to the photos on this list that appear normal at first glance, once we do realize something bizarre is happening, it can be impossible to unsee what we now know. The picture looked completely fine 5 seconds ago, but now it’s been tainted. Why does that happen? Nothing has actually changed except our perception. Alexis C. Madrigal discussed this phenomenon in a piece for The Atlantic. She showed an example of a black and white photo that might look abstract at first glance but actually features a dalmatian. "It is hard to discern a Dalmatian standing among many black spots scattered on a white background because the part of the image corresponding to the dog lacks contours that define the edges of the dog, and the dog’s spotted texture resembles that of the background," Dartmouth cognitive scientists Peter Tse and Howard Hughes wrote about the image. "Many observers find that they first recognize one part of the dog, say the head, which then makes the whole dog’s shape apparent."

But if people ever come across that image of the dalmatian again, they will see it immediately. "When the scene is encountered again, sensory cues will again identify high information areas, but this time the prior knowledge needed to complete the perceptual act is readily available, and the perceptual interpretation is achieved in a way that seems automatic and perhaps inevitable," says Tom Toppino, a Villanova psychologist. "One general lesson of this demonstration is that perception is not the result of simply processing stimulus cues. It also importantly involves fitting prior knowledge to the current situation to create a meaningful interpretation."

Some ambiguous images are “reversible”, like the famous Rabbit-duck illusion, where you might be able to know both are there and flip back and forth between which one you see. But other images can never be seen the same again. "I think one can describe the can't-unsee phenomenon as follows:  Once you interpret visual stimulus in a certain way, you'll continue to interpret it in the same way now and the next time you encounter the stimulus," Toppino says. "Ambiguous figures certainly involve some of the same processes."

We hope you are enjoying this list of photos that might require you to stare at them for several minutes to understand. Just think of them as real life Where's Waldo images. And as for the ones that are more like optical illusions, maybe your fellow pandas can help you understand what's going on in the comments. Keep upvoting the pics that you find most hilarious or confusing, and then if you want to check out even more "when you see it" pics, we've got another Bored Panda piece for you to read next right here.