A smiley face built with SVG animates its eyebrows in a looping motion. The example demonstrates fundamental D3.js DOM manipulation by appending circles for the eyes, rectangles for the eyebrows, and a path generated with the `d3.arc` function for the mouth. The eyebrows move via chained `transition` calls that repeatedly offset their vertical position. The code imports `select` and `arc` from the D3 v5 library and renders entirely in an SVG container.