Bingo. Except in this case it's a whole nest of things. Not TOO bad, all things considered, but this is one multi-headed beast of a game. It doesn't follow the normal debugging rules of regular single-threaded code. If you count the GPU, this thing uses thousands of concurrent threads. Just counting the CPU, it uses dozens.
And we have to use a really light hand with the locks and such, so that means that things can creep in in terms of race conditions that just have to be smooshed once they're found. It's quite a good architecture, but still.
