A smiling cartoon face is drawn with D3.js, built from SVG shapes: a yellow circle head, two eyes, rectangular eyebrows, and an arc-based mouth path. The code uses D3’s `select` and `arc` APIs, with a `group` element centered via a transform. Eyebrows animate by modifying the `transform` attribute through a two-step `transition` chain, moving them down and back up over four seconds total.