Kneading is a common cat behavior. It has its roots in the actions kittens take while still nursing. Kittens place pressure in one spot using the alternating motion of their left and right paws to stimulate milk flow on their mothers. No one is certain why adult cats knead, although theories exist that range from scent marking to stretching.
Returning Affection and Scent-Marking
Nursing was a comforting activity for most kittens. They associate kneading with that comfort. When you're petting your cat and she starts to knead you, she is displaying her feelings of contentment. She is also giving you back that affection.
Most cat guardians know the power of scent for their cats. By rubbing themselves against furniture or shoes, they are laying claim to their territory. Kneading can be another form of scent marking. If your cat is kneading you, she is saying you belong to her.
Creating a Sleeping Spot and Stretching
Way back in their ancestral history, cats would knead to make grass and flowers flat. They created a sleeping spot out in the wild. If your kitty tends to knead you and then curl up in your lap, she has prepped you for her own comfortable nap.
Cats are known for their amazing flexibility and tendency to nap in unexpected places. Kneading, whether it's on your leg or on the couch, could be another way to stretch out the legs and remain limber for those waking hours of play.