Emily Brown
An optical illusion featuring a human face is sending people into spirals as they attempt to work out whether it's moving to the left or the right.
If you're looking for a quick brain challenge, you're in need of a distraction from daily life, or you've just been scrolling for so long that you've found yourself here, then settle in and prepare to be baffled:
Known as the 'hollow mask' illusion, the way you perceive this video taps in to the way your brain is wired, and how humans make sense of the visual world.
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As the video begins, it seems pretty clear that the faces are looking out towards us. If they were 3D, you'd expect to the nose to be protruding towards you - aka, the face is convex.
Logic tells us that as the faces begin to turn to the side, we'd see the back of them. Imagine they're masks - this concave side would be where you'd slot your own face.
However, as the faces actually do begin to turn to the side, all of a sudden they look like they're facing outwards again, and the direction in which they're moving appears to switch.
It's a tough video to get your head around, and has left viewers desperate for answers.
"I'm only seeing it left to right, then right to left?" one person responded after watching the illusion, while another commented: "I just spent 4 straight minutes absolutely lost in this video. why would you do this to me?!?!"
One viewer simply branded the scene 'creepy as s**t', while a fourth responded: "I’ve always seen it moving left (counterclockwise). I can trick my brain into seeing it move the other way, but it defaults to left."
Unfortunately, I don't have an answer for you in terms of which way the face is turning, because I can't tell. But I can explain why it's confusing.
When looking at the illusion, our brains combine what we actually see - known as bottom-up processing - with what prior experience tells us we should see - aka top-down processing.
Danai Dima, of Hannover Medical University, has previously explained: "Our top-down processing holds memories, like stock models. All the models in our head have a face coming out, so whenever we see a face, of course it has to come out."
Even when aware of the illusion, many people's brains still can't comprehend the idea of the face being concave.
Interestingly, previous research has indicated there are some instances when people can 'beat' the illusion, including when intoxicated.
People with schizophrenia are among those who can perceive the 'hollow' face for what it is, with Dima suggesting that patients with the condition may not be able to make the connection between the mask and a normal human face.
Being able to recognise the concave side of the face would help determine the direction the face is moving, though some viewers have also claimed to have cracked the illusion by focusing on certain parts of the moving image.
So, can you figure out which way it's moving?