Why does my cat knead? ?

Every cat I've ever had sit on me knead (and that's quite a few!). Kneading starts when they are kittens, as kittens kneaded their mother to help the milk flow more freely. Kneading is learnt very young, so it is natural that this behaviour is carried on throughout adult-hood. Cats tend to knead when they are happy and content on their owners (kind of like a seond mother) lap.