YouKnowWhat on Instagram: "This clip demonstrates the moiré principle, an interference effect that appears when two repeating patterns overlap with slightly different spacing or timing, creating a larger, slower pattern that doesn’t physically exist in either source. As the ruler vibrates, its fine edge details form a fast repeating pattern. In shadow, the lighting becomes more directional and high-contrast, amplifying small changes into strong light–dark variations. In direct light, reflections