Spendur,
This is an aframestokyo video, but I think it shows what your describing. To save time the approximate 9 to 11 minute mark probably shows the best.
https://m.youtube.com/watch?v=eFMHWpi9gdc
And another without much movement toward the ends of the stone.
https://m.youtube.com/watch?v=6R7zsGj0FEA