A smiley face drawn with D3.js animates its eyebrows in a looping up-and-down motion. The example demonstrates fundamental SVG construction using D3 selections and shape generators, building the face from a yellow circle, two eyes, rectangular eyebrows, and an arc-based mouth. The eyebrows transition vertically via chained `transition().duration()` calls, while `d3.arc` computes the mouth path. The code uses `select` and `arc` from D3 v5, with all elements positioned through SVG attributes.