A smiling face is drawn as a static SVG, then its mouth widens and narrows in an animated loop using D3. The static portion uses basic SVG shapes—a yellow circle with a black stroke for the head and two smaller black circles for the eyes. The animated mouth is generated with D3's `arc` geometry, and its start and end angles are modified over time inside a `d3.timer` callback. The mouth shape is redrawn as a path using the updated arc each frame.