Practice: Back Roll

I sit crosslegged and rock forward and back gently on my sitz bones which are like little rocking chair rockers. It is a small motion. My psoas shifts my viscera and buttocks press along the rug under me. I go slowly for a while, watching my spine responsively arc into a curvature, my weighty head dropping forward then righting. I feel like a sailor on a sea swells. The curve prepares itself in me.