A D3.js smiley face animation demonstrates basic DOM manipulation with SVG shapes. The yellow face, eyes, and mouth are drawn using D3 selections and the `arc` generator, while the eyebrows move up and down through chained `transition` calls over 2000ms intervals. The code uses `select` to target the SVG element, dynamic width and height attributes, and group elements (`g`) to structure the face components. The animation loops by transitioning the eyebrow group's transform attribute back and forth.