A smiling face follows the mouse cursor across an SVG canvas, responding instantly to pointer movement. The example demonstrates a minimal React integration with D3, using React's `useState` and `useCallback` hooks to track mouse coordinates and re-render the circle's position. Rendered as a single SVG circle, it relies on D3 v5's `arc` import, though the visible shape is a simple circle rather than an arc. The code pairs React 16.9 with d3.min.js, updating the circle's `cx` and `cy` attributes via React state on every mousemove event.