A smiley face circle follows the mouse cursor across an SVG canvas, updating its position in real time as the user moves the pointer. The React component tracks mouse coordinates through an `onMouseMove` event handler, storing them in state via `React.useState` and updating the circle's `cx` and `cy` attributes. The visualization uses React 18, D3 v7 for the SVG rendering, and demonstrates simple interactive event handling without any external data source.