A smiling face built from SVG primitives animates in a React app using D3.js v5. The code creates a yellow circle for the face, adds two eyes, and applies a transition to the left eye, moving it vertically over two seconds with `transition().duration()`. A mouth is drawn using the `arc()` generator, and all elements are centered with a translated group. Rendering is SVG, and the animation demonstrates D3’s selection and transition APIs within a React setup.