Why do cats knead?
Article gives two reasons: " 1. in the presence of someone with whom they feel safe ... because they associate the behavior of treading their paws with the comfort they felt when they were nursing<p>2. It's possible kneading can be used to deposit scent... to mark territory."<p>Some dogs like to suckle on your arm (or small squishy) well into their adulthood, so I suppose #1 makes sense.