Tile Floor is Not Good for Scratching

I am lead to believe that Lilly might be somewhat..... dumb. There is no better way to put that. I find myself watching her do somethings that she does and I wonder if it's normal.

She has recently starting to do this...

She will roll over on her back and shake. Now, I don't know why she does this. At first I thought maybe she was having a spasm. But then she did it again and again. I think maybe she's just scratching her back.

The funny thing is she does that on the tile floor in the living room as well. I don't think that helps very much. Tile floor is sort of smooth and not good for scratching.