WHO WROTE WHAT BIT?
Ah. Another tricky one. As the official Keeper of the One True Copy, Terry physically wrote more of Draft 1 than Neil. But if 2,000 words are written down after a lot of excited shouting, it’s a moot point whose words they are. And, in any case, as a matter of honor both of them rewrote and footnoted the other guy’s stuff, and both can write passably in the other guy’s style. The Agnes Nutter scenes and the kids mostly originated with Terry, the Four Horsemen and anything with maggots started with Neil. Neil had the most influence on the opening, Terry on the ending. Apart from that, they just shouted excitedly a lot.
The point they both realised the text had wandered into its own world was in the basement of the old Gollancz books, where they’d got together to proofread the final copy, and Neil congratulated Terry on a line that Terry knew he hadn’t written, and Neil was certain that he hadn’t written either. They both privately suspect that at some point the book had started to generate text on its own, but neither of them will actually admit this publicly for fear of being thought odd.
Good Omens: The Nice and Accurate Prophecies of Agnes Nutter, Witch (2006 edition) – appendix by Terry Pratchett and Neil Gaiman (via horriblybookish)