Kneading is a practice which is in point of fact a reminder of kitten days... From the age of three weeks until weaning kittens spend a great deal of their time kneading and purring near their mothers milk supplying nipples.
Kittens are quick learners when it comes to fun and food. They learn quickly that the movement of their paws on either side of the mother’s nipple stimulates the milk flow to their waiting mouth.
A supple, balmy and relaxed area; be it lap or comfortable sofa cushion laps seem to bring to the surface this kittenish behavior in cats.
For the unsprayed, adult female feline when she is approaching heat she might also display this very same kneading cat behavior. It's as if the surplus hormones activate this instinctual behavior automatically behaves this way.
To test if your cat is going into heat, softly stroke her along the back towards the tail... If she is in heat then she will more than likely elevate the rump area and prepare for the mating position.
Often when you perform the same test to your feline while he/she are kneading on your lap, you might bring out a comparable response. A female nearing heat will be extremely friendly and rub furniture, doorways, etc with her head and neck because many of the sent glands are located. A cat that is not happy will not carry out this paw pushing activity. So if your cat kneads on your lap it means you are a good provider and are loved and trusted by your fabulous feline