Moving Circles is an interactive visualization that generates expanding ring particles that follow the cursor across a dark background. As the mouse moves, the code inserts new circle elements at the pointer position, each with a unique hue from an incrementing HSL color value. The circles then animate outward over two seconds using a square-root easing function, growing from a tiny radius to 100 pixels while fading their stroke opacity to zero before being removed. The example is built with D3 v3, using SVG transitions, mouse event handling, and d3.hsl for color generation.