A single gray circle follows the cursor's every movement across an SVG canvas in this interactive React visualization. The circle's position updates in real-time based on mouse coordinates captured through an event listener. Built with React 16.9 and rendered as SVG, it uses the `useState` hook to track mouse position and `useCallback` to optimize the `onMouseMove` handler. No data source is involved; the example demonstrates basic state management and event handling in a React visualization context.