What you're seeing are standing waves captured through a camera at just the right frames per second (fps). This creates a stroboscopic effect, where the string’s rapid vibrations sync with the camera’s shutter, making the invisible visible. When you pluck a string, it vibrates in both directions those waves bounce back and forth between the fixed ends of the guitar string. In certain conditions, these reflections interfere constructively, forming a standing wave with nodes (points that don’t mov