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Blake Lively shares Magic Eye illusion on Instagram (to promote her new movie, 'The Shallows')

Blake Lively can add something to her list of accomplishments: stumping the internet with an optical illusion.
/ Source: TODAY

Blake Lively can add something to her list of career highlights: stumping the internet with an optical illusion.

In a photo she shared on Instagram Wednesday, Lively posted a Magic Eye optical illusion, a series of repeating dots that hide a 3-D image underneath.

"Here's a throwback to make you smile," Lively wrote in the caption, adding "90s kid" in reference to the fact that Magic Eye books peaked popularity-wise in the '90s. (The illusions even became plot lines on the sitcoms "Seinfeld" and "Ellen.")

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The Magic Eye illusions are more than just nostalgia for those of us who remember the '90s. Formally called autosterograms, they're meant to exercise our eyes' depth perception. In order to see the hidden image, your eyes have to focus in different directions (essentially go cross-eyed).

So what's in Lively's pic? One of her princess-like Cannes gowns? The words, "Oakland booty"?

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Nope. It actually has something to do with the hashtag Lively included, the title of her new film, "The Shallows."

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Still don't see it? We won't spoil it here, but the folks at CNet ran the illusion through an online viewer to find the answer. They've even created a gif revealing the hidden image.

Or, you could just stare at Lively's Instagram until you go cross-eyed.