Do granules of a dental bone graft move around? Like under your interior jaw bone near the extraction site.

Hopefully minimal. One of the reason why the bone graft fail is the instability or movement of the graft. True grafting required graft stabilization with membrane, cages (titanium fixture to protect graft), or screw in the case of block graft. Micromovement of graft will hinder the fibroblast migration and adhesion and interupt vascular genesis. Must achieve good clotting and full closure for graft stabilization.
Possibly. Depending on the graft used, it is possible that you may feel some of the granules from particulate graft after the procedure. The surgeon will place an umber of sutures to decrease any movement of the tissue immediately over the site, but you still may notice or feel the particulate matter. I would be conscious not to play with the tissue in any way, and closely follow the instructions given.
Common to see. The granules of a dental bone graft are very small & it's easy for them to move around in the early stages of healing following the removal of a tooth. We try to keep them in place as much as possible by suturing the site & sometimes placing a membrane to cover them. There is no need to be concerned if you see or feel some granules as the majority of them should still be intact. Follow instruction.