In a course on processing, the topic of animation and interactivity would cover the principles and techniques for creating dynamic, engaging visual experiences that can respond to user input.

1. Basic animation techniques: Students would learn how to use variables, loops, and conditional statements to create simple animations, such as moving shapes or changing colors.

2. Object-oriented programming: To create more complex animations and interactive experiences, students would need to understand the principles of object-oriented programming. This would involve defining custom classes and methods, creating instances of those classes, and using them to manipulate graphical elements.

3. Interactivity: Once students have a basic understanding of animation and programming, they would learn how to make their programs more interactive. This might involve using mouse and keyboard input to control animations and respond to user actions, or creating simple video games that use collision detection and scoring systems.

4. Graphics and visual design: To make compelling animations and interactive experiences, students would also need to develop a sense of visual design. This might include experimenting with color, composition, and typography, as well as understanding the affordances and limitations of the processing graphics library.

5. Project-based learning: Throughout the course, students would likely have the opportunity to work on individual or group projects that apply the concepts they've learned in class. These projects could range from simple animations to more complex interactive installations, and would allow students to develop their programming and design skills in a hands-on way.

Overall, a course on animation and interactivity in processing would help students to develop the skills and knowledge needed to create engaging and dynamic visual experiences that are responsive to user input.