A smiley face built with D3.js demonstrates fundamental DOM manipulation and animation. The face includes eyes, blush, a nose, mouth, teeth, ears, hair, and hands, all rendered as SVG elements. Eyebrows transition vertically using `transition()` and `attr()`, creating a moving expression. The code uses D3 v5 selections, `arc()` for path generation, and `selectAll().data().enter()` to bind data for drawing teeth.