Shows that he’s comfortable with them.  🙂  The kneading is a sign of their contentment for them.  As below:
 
“That loud purring followed by the sharpening of claws on some soft spot of your body is called “milk-treading.” When you relax and sit quietly, you’re giving your cat the same signal he got from his mother when he was a kitten – that his mother was ready to let him suckle. A nursing kitten instinctively uses his paws to draw out the milk, gently pushing on his mother’s stomach to increase the milk flow. When older cats behave this way, it’s a good sign that they’re happy, content, and probably recalling their kittenhood.
 
“Cats can sometimes adopt a blanket and use it like a security blanket. This will include lots of kneading, purring and suckling at the blanket. Kittens who are taken away from their mothers before they are fully weaned may also develop a habit of kneading a human whom they have adopted as a maternal figure, and suckling their ear or shirt. Cats mainly do this as kittens but sometimes it continues into adult life.”
 
My cat used to knead us all the time and would suckle our ears.  She also loved my heavy winter coat because it had a furry inside.  Whenever I would put it down, she’d knead it for a while as if fluffing it like a pillow and then settle down in it.  It was adorable.  🙂