A smiley face rendered in SVG uses D3.js to animate its eyebrows in a looping up-and-down motion. The face consists of yellow circular head, black eyes, a straight mouth line, and rectangular eyebrows, all constructed with D3 selections and SVG elements. The eyebrow movement is achieved through chained `transition().duration()` calls that alternate the vertical position of a group containing both rectangles. The animation runs once per page load, with the code importing `select` and `arc` from the D3 library.