This example demonstrates D3’s exit selection effect by animating a fluctuating number of circles that move along sine-wave paths. Using `d3.select`, `d3.range`, and a `setInterval` loop, it updates the data array each frame, then merges newly entered circles with existing ones via `.enter()` and `.merge()`, while `.exit().remove()` instantly deletes circles that no longer have corresponding data. The visualization uses an SVG rendering with dynamic `cx` and `cy` attributes, showing how D3 manages DOM elements for changing data sizes without transitions.