A single dark circle follows the mouse cursor as it moves across a blank SVG canvas. The circle’s position is tracked using React’s `useState` and `useCallback` hooks, with the `onMouseMove` event capturing the pointer’s `clientX` and `clientY` coordinates. React re-renders the SVG element with updated `cx` and `cy` attributes, while D3’s `arc` function is imported but not used in this rendering logic. The example demonstrates the integration of React state management with D3’s SVG creation capabilities.