Dushka will lie back in my arms, with her head back and legs splayed, inviting me (and only me) to rub her. She is doing this in my siggie. The others are more dignified, though will sometimes lie back with heads on the floor when I am petting them. But sometimes it will turn into rough play and then I have to stop quickly. Dushka will always lie on the floor with claws ready when Persil wants to play.