Animated SVG circles demonstrate live data binding and join updates in D3. The visualization uses `selectAll` with `.data()` and `.join()` to re-render a set of circles every frame, updating their `cx`, `cy`, and `r` attributes based on a sinusoidal function. The code imports `select` from `d3` and defines custom functions `vizData` and `makeData` to generate coordinates and radii dynamically. Runs at 60 frames per second via `setInterval`, producing a smooth wave-like motion across the viewport.