Boids, Game of Life, Genetic Algorithms, Pixel Shaders...

All so satisfying to play with.

One of my favorites was when I was sure I was right about the Monty Hall problem, so I decided to write a simulator, and my fingers typed the code... and then my brain had to read it, and realize I was wrong. It was hilarious. I knew how to code the solution better than I could reason about it. I didn't even need to run the program.