Let's make a face
A smiley face, drawn with SVG circles and an arc path, animates its eyebrows in a looping sequence in a D3.js visualization. The code builds the face by manipulating SVG groups and shapes, using D3's `select` and `append`. A `transition` with a 2000-millisecond duration shifts the eyebrow group up and down, creating the expression change. The face's construction relies on explicit pixel coordinates and D3's `arc` generator for the mouth, with a yellow circle serving as the head.