Your cat kneads you because she needs you. Her cute though sometimes painful behavior is an action that shows love and trust.
As explained in the SciShow video posted above, kneading is a behavior only domesticated cats have taken with them into adulthood. When cats are kittens, they knead their mothers' bellies to stimulate the production of milk. House-trained animals retain some of their more social and "baby-like" behaviors, including kneading, because they receive positive reinforcement over generations.
Basically, cats are free to be their child-like selves because we show them love --- not real-life danger or threat -- when they act immaturely. Knead on, little kitties. You'll always be our babies.
Below you can watch a real cat kneading the belly of HuffPost reporter Andy Campbell. Campbell is not angry with the cat, but with a friend.
H/T Mental Floss
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