Rolling over, that is.  Today, Katie went to yoga, and I stayed at home with Penelope.  When Katie left, Penelope was enjoying being on her back on the play mat.  Since she hadn't had any tummy time today, I flipped her over onto her belly and put her arms under her chest.  She started looking around, and I went to put something away.  When I came back, she was on her back!  Since there was no one else to help her roll, it was clear that she did it herself.  So, I put her back onto her chest to see if she could do it again.  This time I watched her closely.