A smiling face rendered as an SVG circle follows the mouse cursor across a 960-by-500 viewport. Built with React and D3 v7, the component tracks pointer movement via the `onMouseMove` event, updating the circle's `cx` and `cy` coordinates with the event's `clientX` and `clientY` values. The visualization uses React's `useState` and `useCallback` hooks to manage and update the cursor position, with the SVG output rendered directly to the DOM.