I’ve shown pictures of Renn at rest before, but the position he likes best always amuses me. He adopts this position only on furniture with arms (eg. the couch, the armchair, a loveseat). He does sleep on his back elsewhere but only on those furnishings does he lie quite like this. I saw why this weekend. He grabs the front of the arm and uses it to lever his rear end up and around, so that he can have his bum against the back of the seat.
Then he snoozes like this. Sometimes, he’ll wake enough to stretch, and then fall asleep again in an elongated position. He’s a funny beast and if I were boneless (or twenty years old), I would probably enjoy resting like this, too.