A smiling face rendered in SVG uses D3.js to demonstrate fundamental DOM manipulation and animation. The face, composed of circles, ellipses, and a path-based mouth, is assembled through chained `append` calls and coordinate transformations. The most prominent behavior is the animated eyebrows, which move up and down using a `transition().duration(2000)` sequence. This example showcases D3’s core API for selecting elements, applying transforms, and creating simple timeline-based animations without any external datasets.