Why do cats knead?

KC was never really a "kneader" but Shermie does it a lot on the bed's comforter. It's very soft and feels almost velvety; this is the only thing he does it on. Usually at night he'll come onto the bed and instead of laying down to sleep, he'll start kneading on the covers, purring, and drooling - a LOT. Is this a normal thing? I know that lots of cats knead on things but do they all drool this much? And I was just curious why cats even knead in the first place. I heard somewhere that it reminds them of their mothers. True?

It's what kittens do when they're sucking milk from their mom. I guess cats never outgrow the comforting feeling of kneading.

I love nothing more than to see and feel a cat kneading. For whatever reason they do this, it is always a sign of their contentment and happiness.

I have one that is a drooler and he is the only cat I had ever seen drool like he does. It was so strange to me at first I had him into the vet to see if it was because of a problem. She told me that some cats just get a little over excited and tend to drool. She had seen it before even though I hadn't.

I know when Skittles kneeads she is always purring very loud. So I take it she is happy.