Two patterns on top of each other with at least the top one semi transparent will interfere with each other. The points where the two patterns cross each other become the visually dominant pattern called a moire'. This interference pattern or moire' shifts position if the two original patterns move in relationship to each other. If the two original patterns are even slightly separated spatially, and the viewer moves the moire' also shifts because of parallax. Even each eye of the viewer also sees the interference points in different locations.
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