Balls are at least a little less active, I think. We had one experience with mine, back when she was about a year old, where she got out of her tank, while we weren't home, and ranged exactly two feet away, to a pillow that had fallen on the rug, and curled up under it. I had textbooks stacked on top of her new tank, thinking that would be good enough till I got some tank clips...turns out, it wasn't. Not saying that this is a typical experience, but it does speak of a ball's er, lazier qualities. My sweet fat pet rock.