A smiley face built with D3.js animates its eyebrows in a continuous loop. The face is constructed from SVG elements: a green circle for the head, two circles for the eyes, rectangles for the eyebrows, and a path created with the `arc` function for the mouth. The D3 `transition` API moves the eyebrows up and down over two-second intervals. The code demonstrates fundamental DOM manipulation via `d3.select` and `svg.append`, using fixed pixel dimensions and coordinates from the SVG element.