Kai and Skala are close as can be. The German shepherd/husky mixes are not only brother and sister but best friends — and when the pups play together, it’s as if the two become one.

Their dad, Joe, who goes by BeanzMeanzBranston on Reddit, managed to capture this in a brilliant optical illusion that’s been leaving everyone on the internet scratching their heads.

“Kai, the boy, is the dopey one and the instigator,” Joe told The Dodo. “Skala will be laying down sleeping, and Kai will grab her by the tail to tell her it’s time to get up for a little play fight. But if she doesn’t want to, she’ll let him know. Her bark is worse than her bite.”

Recently, the pups were play fighting when Joe snapped a picture of them to send to his girlfriend. When he looked back at the photo, he realized he’d captured a confusing perspective. “I just happened to catch [them at] the perfect time,” Joe said.

He posted the picture on Reddit with the caption: “My dogs share a mouth sometimes.” But even with that hint, Reddit users still struggled to understand where one dog stopped and the other began.

“Some people can see it straight away, some people think it’s a mirror image, some people think it’s Photoshop,” Joe said. “The key is to zoom in on the front teeth. You can see the overlap of the jaws there.”

The unsettling photo sparked a lively debate — some people were sure that the two dogs were one monstrous creature out of a video game. “I feel like if this was some type of IQ test… I most definitely failed,” commented one Reddit user. “I mean, I knew there were [two] dogs. I just still can’t tell where each of them begins or ends,” wrote another.

To help clarify, one Redditor made a diagram showing the outlines of the two dogs.

Life with Kai and Skala is never dull for Joe — and this is just one example of the excitement the two pups bring to their dad’s life.

“They love to run, then they love to sleep,” Joe said. “They’re intelligently disobedient. They know what you’re saying, but that doesn’t mean they’re gonna listen.”