A smiley face rendered as SVG responds to no user input, but its eyebrows perform a looping animation, moving down and up repeatedly. The demo uses D3 v5 selections and transitions to manipulate SVG elements, including circles for the face and eyes, rectangles for eyebrows, and a path for the mouth via the `arc` generator. The code structures the face using a centered group with translated subgroups for the eyes and eyebrows, while `transition.attr` with durations animates the eyebrow group’s vertical position. Built with React, the example runs in a plain HTML page with D3 loaded via CDN.