i'm not sure why picasso carries her tail up like that, but it's not all the time that she does that. i know that wild rats run with their tails and their whole body low to the ground, so maybe it's just a kind of scampering they do when they feel safe? maybe it's a dominance thing? wheelie tail is a completely different look, so even though picasso runs in her wheel a lot, i don't attribute her upright tail to the wheel at all. picasso kind of always carries her tail above the ground, though not always as high as in that picture, and she is definitely the more outgoing of my girls. maybe it's just a perky personality thing?