A dynamic SVG animation demonstrates D3's data join pattern with shifting circle counts. The visualization uses `d3.select`, `d3.range`, and the `selection.join()` method to bind an array of computed data points to circle elements, updating their `cx` and `cy` attributes with sine-based positions. Circles appear and disappear as the data length varies, driven by a `setInterval` callback that increments a time variable at 60 frames per second. The example renders directly into the browser using D3 v6, with no external data source beyond the generated numeric values.