A smiling face made of SVG shapes demonstrates fundamental D3.js DOM manipulation. The code selects an SVG element and appends yellow circles for the head and eyes, black rectangles for eyebrows, and an arc-based path for the mouth. Using `d3.transition` with a two-second duration, the eyebrows animate upward and then back down, creating an expressive movement. The example uses D3 v5's `select`, `append`, and `attr` methods to build and update elements, with the mouth drawn via `d3.arc`.