A fork of the "Double Harmonic" example animates a small black circle tracing a complex path composed of two overlapping circular motions. The code uses D3 v6 selections and joins to render and update SVG elements every 50 milliseconds, calculating the circle's position with sine and cosine functions driven by two radii and a time step. It draws the path as two connected lines from the center to the ball, while a larger blue shadow circle marks the moving point. This visualizes parametric motion and harmonic oscillation in an abstract, looping animation.