Have you ever seen something that looks so realistic, so natural, that your brain couldn't comprehend it when a knife comes and cuts it in half and it turns out to be made of cake? 

Millions of viewers have watched  as TikTok  bakers slice or bite into inedible-looking objects with fluffy, frosting-filled innards … or have tuned into Is It Cake?, the aptly named Netflix show. Why? 

As a form of entertainment, this kind of visual trick is hardly new. For centuries, artists have delighted in fooling us into thinking one material is another. From Michelangelo’s marble David, with his sinewy, soft-looking flesh, to Giovanni Strazza’s Veiled Virgin, draped in a marble veil that appears gossamer thin. What makes these illusions so mesmerizing? Maybe it’s because these classic works of art and these modern social media ruses test our ability to use an underappreciated skill that’s been essential to our species’ survival: identifying what stuff is made of.

Over the past century, neuroscience has made great strides in understanding how the brain visually identifies objects—like mugs, trees, and faces. But the question of how we recognize what those objects are made of (smooth porcelain, rough bark, soft flesh) has been overlooked until relatively recently. 

“Our world contains both things and stuff, but things tend to get the attention,” wrote Edward H. Adelson, an MIT neuroscientist whose provocative 2001 paper, “On Seeing Stuff: The Perception of Materials by Humans and Machines,” spurred a flurry of material perception research.1

“Yet materials are just as important as objects are,” he wrote. “Our world involves steel and glass, paper and plastic, food and drink, leather and lace, ice and snow, not to mention blood sweat and tears.”

Recognizing what an object is made of tells us—as it told our ancestors—how we can interact with it: Can we squeeze it? Eat it? Touch it without getting burned or scratched? Pick it up? (And if so, using how much force?) Material perception helps us spot the glimmer of potentially potable water, and sort firm, fresh-looking fruit from wrinkled, rotten ones. 

Humans, like chimpanzees, use material properties like hardness to determine if a rock is a suitable weapon or tool. And brains that are optimally tuned to making these sorts of decisions efficiently and accurately are essential to survival and reproductive success, especially as our evolutionary predecessors navigated the travails of early human history.

There's a lot more to the story, so click that link and learn why we enjoy being tricked… by cake!