Went down the rabbit hole on this. Cats are hardwired to kill small, squeaking things. Their own newborn kittens are small, squeaking things. The only reason a mother cat doesn’t eat her babies is a hormone that shuts off her hunting brain the moment she gives birth. That hormone is called prolactin. It’s the same one that triggers milk production. But it also cranks up her protective aggression and dials down her urge to hunt at the same time. The more prolactin in her system, the harder she’ll fight for her nest. And the less likely she is to see anything small and warm near that nest as food. This is the entire reason cats adopt puppies. When a nursing cat finds a puppy or a baby rat or a chick near her nest, the animal is small, warm, and isn’t trying to escape. Her hunting instinct doesn’t fire because prolactin has it suppressed. So her brain goes to the only option left: that’s my baby. In Jordan, a cat named Nimra raised seven chicks alongside her four kittens. In Brazil, a mother cat found abandoned newborn puppies and nursed them with her own litter. Animal shelters actually exploit this. At the Animal Care Centers of New York, staff place orphaned kittens with nursing moms who start feeding them on the spot. Researchers tracked over 200 stray cats across 72 nesting spots on Ainoshima Island in Japan. Every single pair of mothers that could have nursed each other’s kittens did. All of them. 8 out of 9 pairs shared the same nest. Cats who weren’t nursing brought food to the ones who were. Kittens in these group nests grew up about 10 days faster than kittens raised by a single mom. Stray cat colonies are run entirely by mothers and daughters. They nurse each other’s kittens, groom them, guard them, and never bother figuring out whose is whose. Even spayed cats who’ve never given birth can start producing milk if a kitten latches on, because the hormone drop from surgery mimics the hormone drop after giving birth. A 2025 study found that when you gently pet a cat, a bonding hormone called oxytocin spikes in your brain and the cat’s brain at the same time. But only if the cat came to you first. Grab the cat, and the hormone drops.