Moiré patterns are formed when two grids or line drawings are superimposed. The intersections of the lines create new patterns not present in the originals. This figure contains two drawings consisting of lines radiating from a point. One drawing is fixed and the other moves thus generating a changing interference pattern of circles that cross both points.
The animation can be stopped or re-started by pressing SHIFT and clicking on the pattern. You can also click-and-drag to control the motion of the pattern manually.