Cats can’t smile the way humans do, since their facial muscles aren’t built for it, but a kitten’s relaxed, half-closed eyes, soft mouth, and tilted head can look exactly like a smile to us, and that’s not an accident of our imagination. Researchers call this the ‘baby schema’ (Kindchenschema), a set of infant-like features, like big eyes, a rounded face, and soft curves, that evolutionary biologist Konrad Lorenz first described in 1943 as triggering automatic caregiving responses in humans. When a kitten’s face hits those proportions, our brains respond with the same reward and bonding chemistry activated by human infants, which is part of why a single ‘smiling kitten’ photo can rack up millions of shares in a day.