Animating data changes in your visualizations brings them to life and helps users understand updates more easily. D3 makes this possible through its transition methods, which allow you to smoothly interpolate between attribute or style values over time. To start an animation, you use the transition() method on a selection. Once a transition is started, you can control how long it lasts with duration(milliseconds), and you can fine-tune the pacing of the animation using ease(easingFunction). The duration determines how long the transition takes to complete, while the easing function shapes the speed curve of the animation—making it accelerate, decelerate, or bounce, for instance. By chaining these methods with attribute or style changes, you can create highly interactive and visually appealing charts that update gracefully as your data changes.