This example demonstrates how D3.js can build an animated smiley face from SVG primitives, showing a yellow circle head with black eyes, arched eyebrows, and a mouth. The eyebrows transition up and down repeatedly over two-second intervals using chained `transition().duration()` calls. The code uses D3 v5 selections, the `arc` generator to create the mouth path, and SVG attribute binding for positioning. All elements are centered dynamically using the SVG’s width and height, with facial features offset by fixed pixel values.