A circle follows the mouse cursor as it moves across an SVG canvas. The React component tracks pointer coordinates via an SVG `onMouseMove` event handler, updating the circle’s `cx` and `cy` attributes through state. D3’s `arc` import is unused here; rendering relies on React’s `useState` and `useCallback` hooks with a plain `<circle>` element. The visualization demonstrates real-time event-driven SVG updates in a React-D3 hybrid setup.