A smiley face drawn with D3.js animates its eyebrows bobbing up and down in a looping transition. The example demonstrates basic SVG shape creation and DOM manipulation using D3 selections, appending circles for the eyes, rectangles for the eyebrows, and an arc-generated path for the mouth. The `transition()` method with a 2000-millisecond duration moves the eyebrow group vertically, then reverses the transform to create the oscillation. It uses D3 v5's `select` and `arc` APIs.