A large blue circle follows the mouse cursor as it moves over an SVG canvas. The visualization uses React's `useState` and `useCallback` hooks to track the pointer's `clientX` and `clientY` coordinates, updating the circle's `cx` and `cy` attributes on every mouse move. The circle is rendered as a literal SVG `<circle>` element with a fixed radius of 30 pixels, centered initially at the middle of a 960×500 viewport.