Circles move vertically in a wave-like pattern, with their size and vertical position oscillating sinusoidally, creating a flowing, animated composition. The number of circles varies over time, dynamically increasing and decreasing, which demonstrates D3's enter, update, and exit behavior for managing the SVG circle elements. The code uses D3's `select`, `range`, and the `join` API to handle the data binding and transitions, with a React import pattern visible through modules like `vizData` and `makeData`. The animation runs via a `setInterval` loop, rendering as an SVG with a 60 FPS refresh rate.