Mutt TF?

Dog pics might seem rather self-explanatory — however, internet users have been howling over a recent photo of a canine in an unusual position.

Viewers struggled to figure out which end is “pup.”

First shared on Instagram last week by @TheMuffReport, the eye-nigma is blowing up online.

“Why did it take my brain so long to figure out what was going on in this pic?” reads the caption of the image, which appears to depict a dog with a harness.

While this seems easy to read on its face, the difficulty lies in determining which way the doggo is oriented.

The perspective makes it so that the location of the dog’s body, eyes and other parts are not initially clear — making it seem like the animal is a radioactive mutant or a dog placed in a hall of mirrors.

Viewers were understandably stumped by the canine brain teaser.

“Yep 100% saw a Chernobyl dog,” said one baffled commenter, while another wrote, “I’m not sure how long I’m supposed to look before I figure it out. But it hasn’t happened yet.”

“100% John Carpenters ‘dog’ from The Thing,” declared a third, referencing the alien-infected pooch from the 1982 horror classic.

Give up yet? As some astute viewers pointed out, the trick is to turn one’s device upside down, after which viewers will — hopefully — be able to see that the dog has its back arched and head turned to the side.

The initial indecipherability is due to a variation of a phenomenon called the Thatcher Illusion.

Named after Margaret Thatcher, the former prime minister of the UK, this effect describes how it’s difficult to spot changes in features in an upside-down face, even as they are obvious in an upright one.