A smiley face, rendered as SVG elements, demonstrates fundamental DOM manipulation with D3.js. The face's eyebrows animate by repeatedly shifting their vertical position via chained `transition()` calls, each lasting two seconds. The code uses D3's `select`, `append`, and `attr` methods to build the circle, eyes, and rectangular eyebrows, while an `arc()` path creates the mouth. The animation loops the eyebrows up and down continuously.