A smiling cartoon face built with SVG animates its eyebrows in a looping up-and-down motion. The example demonstrates D3 v7 selection and transition methods, using `d3.select`, `d3.arc` for the mouth path, and chained `transition().duration()` calls to move the eyebrow group. The yellow circle face, eyes, and rectangular brows are positioned with static attributes, while the transition animates the brow group’s transform offset. It illustrates basic SVG shape creation and timed attribute interpolation within a single D3 script.