A single black circle follows the mouse cursor across an SVG canvas, with React tracking pointer events to update its position. The example uses React's `useState` and `useCallback` hooks to store the `clientX` and `clientY` coordinates on every `onMouseMove`, re-rendering the circle's `cx` and `cy` attributes. Rendered via ReactDOM into a 960×500 SVG, it demonstrates a minimal interactive data-visualization pattern without any external data source.