A grid of 15 circles undulates vertically in a sine wave pattern, their radii pulsing in a related but offset rhythm. The animation runs on a timer, incrementing a time variable that shifts each circle’s y-position and radius via the sine function. Built with D3.js 6.6.2, it uses the `select` and `range` APIs to create and update SVG circles, adjusting `cx`, `cy`, and `r` attributes per frame.