Indeed, once you start seeing these faces peering back at you, they start to appear everywhere. Some of these objects clearly bear a certain similarity to the emoticons we often use to represent feelings – the curved line of a smile and two circles representing the eyes. But sometimes strange creatures can peer out at us from the sparsest details. In one of Lee’s studies, subjects were shown random grey patterns – similar to static on a TV. Given some subtle priming, they reported seeing a person about 34% of the time. Any contours that appeared in the images would have been extremely fuzzy – yet somehow, the brain was conjuring the illusion that a person was staring back. “It turns out it’s pretty easy to induce this phenomenon,” says Lee.

Although we tend to think that our eyes faithfully report whatever is in front of us, the retina records an imperfect and confusing image that needs to be tidied up by the brain. And Lee thinks this “top-down processing” by the brain is what leads to pareidolia.

One way the brain makes sense of the mess is by making predictions about what we will see, based on our past experience, and then subtly projecting those expectations onto what we see. That way, it can piece together a clearer picture, even if the scene is obscured by poor lighting or fog, say. But it also makes our vision more subjective than you might think – in a sense you really do see what you want to see.

To test his hypothesis, Lee scanned participants’ brains as they looked at those images of grey “static”. As you would expect, Lee found high activity in the primary visual cortex as people started to pick apart the various aspects of an image, such as its colour or contour. But he also saw the frontal and occipital regions fire into action when the volunteers thought they saw a face, and these areas are thought to deal with higher-level thinking – such as planning, and memory. So this burst of activity may reflect the influence of expectation and experience, as predicted by Lee’s “top-down processing” theory. That, in turn, seems to have triggered a region called the right fusiform face area – the part of the brain that responds to actual faces, which may reflect the uncanny feeling that we are looking at a real thinking and feeling being. “If that’s activated, we know they really are ‘seeing’ a face,” says Lee.

That might explain why these faces produce the same subconscious reactions we have when we look at a real person. Last year, for instance, a team of Japanese researchers found that we begin to track the gaze of the phantom faces – in just the same way that we try to follow the eyes of a person in front of us. In other words, whenever you see this perplexed building giving the side eye, you might find an urge to see what’s making him gawp.