Ah, I think you're describing the famous back-squirm. Pongo's routine in the morning is to lie at the bottom of the stairs waiting for his dad to come down. Then he throws himself down for: (a) tummy rub; (b) morning facial - massage of cheeks and ears; (c) back squirm; (d) a moment of complete zen stillness - we think he running down his mental checklist of "have I done everything now?"; (e) jump up on all four feet and shake. Right, ready to go round the garden for a pee now. C'mon.
I think so to -- Cassie does it very often after her morning walk, before settling down for a snooze. She jumps up onto the little sofa, performs a sort of head stand up the back, then wriggles down and along the seat with just that expression on her face. The routine has been performed for today, I'll try to photograph tomorrow
