Aside from some gravid behavior, possibly just temp. regulating. I've had some occassionally be almost completely upside down, but thinking about it, I haven't seen this behavior since getting rid of that rack system. At first sight, I honestly thought they were dead they were that rolled up. Still have all those animals though, so don't think you should be worried if nothing else seems wrong. I haven't had that rack system since 02' or 03'???