Describe how to implement an animation that reacts to user input, like a drag or a scroll.

To implement an animation that reacts to user input, such as a drag or scroll, you can use the GestureDetector along with an AnimationController. The GestureDetector captures user input events, and the AnimationController manages the animation's state. By combining these, you can create dynamic animations that respond to user interactions, enhancing the user experience in Flutter applications. Understanding how to integrate gestures and animations is crucial for building interactive and engaging Flutter interfaces.