A smiling face drawn in SVG animates as its eyebrows repeatedly rise and fall. The example demonstrates fundamental D3.js DOM manipulation by using `select`, `append`, and `attr` to construct circles, rectangles, and a path for the mouth, with an `arc` generator for the smile. The eyebrow motion is driven by a two-stage `transition` with a two-second duration each, moving a group element vertically to create the expressive loop.