A smiling face rendered in SVG uses D3.js to build its geometry, including a yellow circle, two eyes, a mouth via `d3.arc`, and rectangular eyebrows. A `transition` on the eyebrow group animates their vertical position over two seconds, moving them up and down repeatedly. The code employs `d3.select`, `d3.scaleLinear`, and attribute setters to construct the scene, with a fixed SVG canvas sized 960 by 500 pixels.