A smiling face drawn with SVG updates its eyebrows by animating a group containing two rectangles over four seconds. The example demonstrates fundamental D3.js DOM selection and manipulation, using `d3.select`, `append`, and chained `transition` calls with `attr` to shift the eyebrow group vertically. The face is composed of a yellow circle, two eye circles, and an arc-shaped mouth generated with the `d3.arc` helper.