D3.js constructs an animated smiley face by manipulating SVG shapes. A yellow circle forms the head, with two static eyes and a mouth drawn using the `arc` path generator. The eyebrows, rendered as rectangles, animate upward and downward over two seconds using chained `transition().duration()` calls on the SVG group, demonstrating fundamental DOM selection and attribute mutation. The code uses the `select` API to target the root SVG element.