A smiling face drawn with SVG shapes animates its eyebrows up and down in a looping transition. The example uses D3 v4 selections to append circles for the eyes, rectangles for the eyebrows, and a path generated with the `d3.arc()` API for the mouth. All elements are centered within an SVG using a group transform, and the eyebrow motion is driven by chained `transition.attr()` calls on the group’s transform attribute.