A smiling face built from yellow and black SVG shapes animates its eyebrows upward and downward in a looping motion. The example constructs the face with D3 v6 selections, positioning eyes as circles, eyebrows as rectangles, and a mouth as a path generated by the `arc` generator. Transitions chain two 2-second `transition` calls on the eyebrow group to move it vertically, creating the expressive blink-like effect within the fixed 960×500 viewport.