Hanna has roached (in greyhound lingo, it is the position assumed by the pup with the belly up, like a dead cockroach) ever since we got her. She usually does it with one front leg extended up in the air. According to the "hubbypedia" (my hubby, the walking encyclopedia, I guess he will ask me to take this line down when he reads this ;D), greys roach when they are happy.
Louie has never roached. I attributed this to the unevenness of his back, or so I thought. But he is a happy puppy who thinks everybody wants to pet him. Then I started noticing that once or twice a year for a couple of years now, he would try it but very briefly. He usually stops if I make a big fuss out of it. Yesterday was a breakthrough, he finally roached for a while and allowed me to "document" it. I know, big deal. It is for me ;D
It is amazing to realize that the family room has really evolved into the critter room. Last time we sat on this couch was years ago when I was still anal enough to cover it. But the pups love it and we are glad they share such a valuable resource.