A yellow smiley face with eyes and a mouth follows the mouse cursor across an SVG canvas. The React app tracks pointer movement via the `onMouseMove` event, updating the face's position through `useState` and `useCallback` hooks. The face is composed of reusable React components (`Face`, `Eyes`, `Eye`, `Mouth`), with the mouth drawn using a `d3.arc()` path generator. The rendering is entirely SVG-based, with a single `<circle>` for the face, two smaller circles for eyes, and a filled arc for the mouth, all positioned relative to the current mouse coordinates.