You paint a figure from point A to point B. Then It just starts from point B to paint the same figure you painted (same speed and all). At same time it removes from A side what is repainting at B side.

If you manage to paint a figure that starts and ends at the same point, then it stays in place and seems to be a static draw.

If you just draw a straight line, it just starts "to move" forward.

I think it's a combined vector of the drawing action - i.e. a true circle stays in place.

It simply redraws the shape from the last point.