A mind-bending optical illusion circulating on social media is putting viewers' attention to detail to the ultimate test -- and most people are struggling to crack it.

The image, which recently went viral after being posted to TikTok, features what appears to be a straightforward scene: a sailor gazing out to sea. But hidden within the image is the face of his wife -- and it's nearly impossible to find unless you know the trick.

These types of visual puzzles are known as optical illusions. They're images that manipulate how our brains interpret visual input, causing us to see things that aren't actually there -- or to miss what's right in front of us. It's all about how our mind fills in the blanks based on familiar patterns and expectations.

This particular illusion has viewers scratching their heads. It's being described by some as one of the most difficult puzzles online. Reportedly, only 1% of viewers are able to identify the sailor's wife within the first 15 seconds.

The challenge has sparked a flurry of reactions online. While some users instantly spotted the hidden face, many others were left bewildered, wondering where exactly the woman is supposed to be. One TikTok commenter called it "the trickiest" illusion they'd ever seen. Another offered a useful hint: "Turn your phone upside down."

That tip has helped a lot of frustrated viewers finally see the secret hidden in plain sight.

So what are you looking for? It's not a full body -- just a face. The key is to shift your perspective. When the image is flipped upside down, the features of the woman's face become much clearer.

Still can't find her? Look closely between the sailor's legs and the base of his telescope. That's where her face is cleverly concealed, blending seamlessly with the shapes and lines of the surrounding elements.

The puzzle has sparked thousands of comments and sparked debate about whether it's even fair. "Didn't need to rotate it -- saw her right away," one viewer bragged. Another admitted, "Even with the hint, I was lost."

Optical illusions like this aren't just fun distractions -- they're also great mental workouts. They challenge your brain to think differently and force you to break away from assumptions.

Whether you spotted the sailor's wife immediately or needed a little help, one thing's for sure: this viral brain teaser proves that sometimes, seeing isn't always believing.