A smiley face drawn with SVG circles follows the cursor inside a 960 by 500 canvas. The React component tracks mouse movements via an `onMouseMove` handler, updating state to reposition a single circle. While the static markup comments include a complete face, the active code renders only the follower circle using React's `useState` and `useCallback`. The example demonstrates combining React's declarative updates with D3's SVG scene graph for interactive visualizations.