A yellow smiley face drawn with SVG elements follows the cursor as it moves across the screen. The mouse position is tracked via React's `useState` and `useCallback` hooks in response to an `onMouseMove` event on the root `<svg>`. The face is composed of reusable React components (`BackgroundCircle`, `Eyes`, `Mouth`, `Nose`) using `d3.arc` for the mouth path. The rendering is entirely SVG-based, with the face's geometry parameterized by props passed from the parent `App` component.