A smiling face built with SVG in D3.js animates as its eyebrows and pupils shift side to side. The example demonstrates fundamental DOM manipulation by directly selecting SVG elements and appending circles, rectangles, and a path for the mouth, with the mouth drawn using D3's `arc` generator. Animated transitions change the position of the eyebrows and pupils over two-second intervals, while static attributes set the face's yellow fill and black stroke. The code relies on D3 v5 and shows how to chain selections and transitions without data binding.