Ruby does that a lot, some days or months more than others. Some times months before she is at it again. She's been to numerous vet appointments with no worries or indication that it is anything other than an itch.
Its kind of like when we women have an itch, you know down there and unlike a man who just goes for it, junk in hand. We with our dignity in tact do the little
wiggle dance. Well I would imagine it is the same with our pups who by the way have no fingers to itch with.
DH tells her to "Quit molesting the carpet"