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Brick wall

Hole in a cat

Dude, where's my phone?

Cylinders or squares?

Shark bites

The Dress

Woman on Mars

Howling wolf

Cat going up or down?

3D lamps

Ghost ship

Saturn's split moon

Hand it to this illusion

Sometimes our minds play tricks us on, especially when we're faced with a compelling visual illusion. Sometimes those illusions get loose on the internet, sparking endless tweets and Facebook posts about our triumphs and frustrations in sorting them out.

This seemingly dull photo of a brick wall sent the internet into a conniption last month as it spread through social media. There's something else in the photo besides a stack of masonry. Some people see it almost immediately, for others it takes some time. Don't worry. Once you figure it out, you won't be able to un-see it. And, yes, it's pretty silly.

Caption by / Photo by Arron Bevin

This adorable cat entertains followers on Twitter. Owner Hanamomo keeps up a feed of kitty photos, but the markings on this particular cat make it a star. The buff-colored spot on its side is perfectly edged in black, making it look like it has a 3D hole where you can see the desert beyond. The fancy feline is especially popular with Japanese Twitter followers, who discovered its unusual coloration last month and quickly shared the photos around the social-media site.

Caption by / Photo by Hanamomo

This Facebook post turned into a social-media frenzy. The challenge is finding the cell phone hidden within the image of a white table on a floral carpet. It may drive you nuts, but you won't be able to look away until you locate it.

Caption by / Photo by Screenshot by Amanda Kooser/CNET

The Best Illusion of the Year contest from the Neural Correlate Society is a gold mine for mental tricks. This illusion, called "Ambiguous Cylinder," was a runner-up for the 2016 contest. It comes from Kokichi Sugihara, an engineering professor at Meiji University in Japan. The illusion involves some very square-looking objects that appear to be totally cylindrical in a mirror.

Caption by / Photo by Video screenshot by Amanda Kooser/CNET

This may look like a bunch of blue fuzz, but it's actually an optical-illusion image done in the style of a Magic Eye puzzle. Magic Eye illusions flummoxed and delighted lots of people during their heyday in the 1990s. Actress Blake Lively posted this puzzle to her Instagram account in June to promote her work in a shark movie called "The Shallows." If you're good with Magic Eye, then you'll probably be able to see the shark hidden here.

Caption by / Photo by Blake Lively

It's known simply as "The Dress." A photo of a two-toned frock sent the internet into a froth last year as people disagreed about whether it was white and gold or blue and black. Everyone from scientists to celebrities shared their thoughts on The Dress and how so many people could have such different views of its colors. It comes down to how your brain interprets the photo, but it's more fun to argue your viewpoint than agree to disagree.

Caption by / Photo by BBC/YouTube screenshot by Chris Matyszczyk/CNET

NASA's Spirit rover delivered an image in 2007 showing a view of craggy rock formations across the surface of Mars. One dramatically shaded formation stands out as it looks like a small statue of a walking woman. UFO blogs hailed it as a figure made by aliens, but the Planetary Society was quick to call the object an optical illusion and an example of pareidolia, the tendency for our minds to assign familiar patterns to random shapes or sounds.

Caption by / Photo by NASA, arrow added by CNET

This is a wolf, right? Take a closer look. What appears to be a howling creature is more than meets the eye. This is the work of master bodypainter Johannes Stötter. A short video titled "The Wolf" reveals the image's secrets as you see three people emerge out of the body.

Caption by / Photo by Video screenshot by Gael Fashingbauer Cooper

Here's a picture of a cat walking downstairs. Or is it upstairs? That's the question that plagued the internet in April 2015 as people tried to decide which way the kitty was going. It probably helps that the photo circulating online is of a pretty low quality, which obscures any clues to the orientation. So which way is the cat going? That's up to you to decide.

Caption by / Photo by screenshot by Chris Matyszczyk/CNET

These lamps from Studio Cheha look like they sport modern interpretations of classic shade designs, but there's a trick under way. Look at them from the side and you'll see they are actually made from flat acrylic glass etched to make them appear 3D from the right angles. Backers successfully funded the lamps on Kickstarter in late 2015.

Caption by / Photo by Studio Cheha

This photo is a still from a video. It might not look like much at first glance, until you realize the boat in the center appears to be floating above the water. What's happening here is a type of mirage. The video is only a few seconds long, but that's plenty of time to witness the strange sight of a magical boat hovering out on the ocean. YouTube user Friends N Feeders originally shared the video in early June.

Caption by / Photo by Video screenshot by CNET

This NASA photo didn't result in any social-media arguments, but it's still a looker. It shows Saturn's moon Dione as seen by NASA spacecraft Cassini. The perfect angle of Saturn's rings make it look like the moon is sliced in half and could be opened up like a plastic Easter egg. Cassini snapped the image in late 2015.

Caption by / Photo by NASA/JPL-Caltech/Space Science Institute

Art student Dain Yoon has a knack for creating fun illusions using her own body and some carefully applied makeup effects. In this image, she holds her hand over her face, but the hand seems to blend into her features as though it's transparent. Her top-notch painting skills make it work.

Caption by / Photo by Dain Yoon
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