This ‘Scintillating Grid’ swells on mousemove / touchmove.
About ‘Scintillating Grid’ Illusion:
Black dots appear to form and vanish at the intersections of the gray horizontal and vertical lines. When focusing attention on a single white dot, some gray dots nearby and some black dots a little further away also seem to appear. More black dots seem to appear as the eye is scanned across the grid (as opposed to focusing on a single point).
** Curiously, the effect of the scintillation is lessened by cocking the head 45° **