tanais's Leonberger (lean-on-berger) was leaning up against me in the kitchen so I could pat his head and scritch under his chin; his tongue was hanging out so sbisson assures me he was enjoying it even though his tail didn't wag (I only speak a limited dialect of Dog). I told Jago that was enough and stepped backward - at which point he very gracefully slid to the floor once my leg was removed... In a cat this would be enormously funny and a Badge of Shame. For a dog it seems to be a way to expose the stomach for patting. (In a cat that's getting all four sharp and pointy things facing the same way to reward you for laughing).