This example shows a smiley face rendered as an SVG circle that follows the mouse cursor inside a fixed 960×500 viewport. The code uses React’s `useState` and `useCallback` hooks to track the pointer’s `clientX` and `clientY` coordinates, updating the circle’s center position on every mouse move. The face itself is drawn with basic SVG `<circle>` elements—a yellow head and two black eyes—embedded directly in the React component’s JSX. Mouse tracking is handled via an `onMouseMove` event on the root SVG element, with ReactDOM rendering the entire interface.