A circle follows the mouse cursor across an SVG canvas, with its position updating in real time to mirror the pointer’s coordinates. The example uses React state and a `useCallback` event handler to capture mouse movements and re-render the circle’s `cx` and `cy` attributes. Rendered as an SVG element via ReactDOM, the visualization demonstrates a simple interactive binding between user input and graphical output, leveraging D3 v5 only for the underlying scripting environment.