They love being on their backs! Shira gets on the floor of the cage on her back and then pulls herself all around the outside of the cage. I don't know if she is scratching an itch, like a cow scratching itself on a post, or what.
LOL! Libby lays on her back a lot too! She plays with her feet, mumbles to herself, plays with her toys -- so cute! She also lays on her back in her daytime "nap" tent (she takes a nap after lunch when we do). She'll lay in there, talking to herself, for a long time! ("Make a Poop, Make a Poop, Maka, Maka, Maka; Step Up, Step Up, Baby, Baby, Baby" etc.) They much like the sound of their voices!