This example demonstrates how to build an animated smiley face using D3.js, with eyebrows that move up and down over time. It shows fundamental DOM manipulation by selecting SVG elements and appending shapes like circles, rectangles, and an arc-based mouth. The code uses `d3.select`, `d3.arc`, and chained `transition.attr` calls to animate the eyebrow group’s vertical position. The face is drawn entirely with SVG, centered in a 960×500 viewport, and the animation runs continuously without external data.