A smiley face built with SVG is animated so its eyebrows move, demonstrating fundamental DOM manipulation in D3.js. The example uses a linear color scale with `d3.interpolateHcl` for the gradient background and D3’s selection methods to bind and update elements. The code also loads a hierarchy dataset and applies `d3.pack` for circular packing, though the visible rendering focuses on the animated face. Rendering is SVG-based with transitions, shown via a video and live code.