Twenty colored circles undulate vertically across the full screen, their radii pulsing and colors randomly changing at 60 frames per second. This animation demonstrates d3 selections and data joins, where a static `range(20)` array is repeatedly re-bound to existing circle nodes via `selectAll('circle').data(data)`. Using d3 version 6.6.1, the `enter()` selection appends new circles with random fills, while the update selection adjusts `cx` and `cy` attributes based on a sine wave offset by time `t`. The SVG renders in the browser body without margins.