A circle follows the mouse cursor across an SVG canvas, updating its center position in real time as the pointer moves. The visualization uses React's `useState` and `useCallback` hooks to track mouse coordinates via an `onMouseMove` event handler on the SVG element. The circle is rendered as an SVG `<circle>` element with a fixed radius, while the component imports the `arc` function from D3 v5, though it is not used in the displayed logic. The initial circle position is centered at (480, 250) on a 960×500 canvas.