I finally saw Roxi in the act of rolling over. Hoo boy, she's a swirly girl these days. Anyway, she achieves her back-to-stomach motion by wedging one of her feet between the crib slats and giving a kick. Our friend Scott noted that she must be very advanced to already be using tools to achieve her goals. But with a dad like Rob, I would be more surprised if she DIDN'T start using tools at an early age.
The funny thing is that she doesn't roll from her stomach to her back. She's done that on a few occasions, but not regularly. Nowadays, when we put Roxi on her stomach for exercise, she does quite the opposite. Instead of working her neck and back muscles by pushing up, she puts her head to the side and sucks her fingers. If we let her stay like that, she'd put herself to sleep. Very cute, but not useful for muscular development.
It's OK though, she's getting plenty of exercise in different ways. She loves being carried upright, so she can look over our shoulders - into mirrors, at the cats, around the room, whatever. Roxi is taking it all in these days. She turns her head to follow things with her eyes and ears. She also can sit up (with gobs of assistance) and now prefers that to laying in her play gym. She also digs being held up "standing" - she can support her own weight for several seconds at a time. Her legs get unpredictably wobbly though, so we're a ways away from marathon training.