This is a recent development. She grabs little fistfuls of skin and digs in her nails. She is doing it in a playful way but it really hurts and is beginning to upset our 4yo ds. We didn't experience this with ds - just a short phase of biting for which we responded by putting him down and/or walking away. Is this pinching behaviour common? There doesn't seem to be any pattern to it and I'm not sure what if anything we should be doing about it. Has anyone else experienced this?