why does my dog chomp on his blanket while moving his paws?

Why does my dog suck on his blanket?
My dog lays down with his blanket, pulls and tugs on it until he forms a ball shape and then he starts sucking and chewing on it. He actually zones out while doing it, like he might get if dogs could take drugs. Why does he do this?

I would take that as a sign he was separated from his mom too early - he's suckling on his blankie...