It turns out that understanding how big-bang works is harder than I thought. A key concept that’s not obvious is that big-bang does a lot of the work for you. Your job is

After that, big-bang does all the work of keeping track of the mouse, changing one state into another, and drawing the state as a kind of animated flip book.

I’ve been told by the Big Chief Racket that the Racket Documentation is not the best way to learn big-bang. Here are some better places to get information: