Most of what we get up to in the Laundry is symbolic computation intended to evoke decidedly nonsymbolic consequences. But that's not all there is to...well, any sufficiently alien technology is indistinguishable from magic, so let's call it that, all right? You can do magic by computation, but you can also do computation by magic. The law of similarity attracts unwelcome attention from other proximate universes, other domains where the laws of nature worked out differently. Meanwhile, the law of contagion spreads stuff around. Just as it's possible to write a TCP/IP protocol stack in some utterly inappropriate programming language like ML or Visual Basic, so, too, it's possible to implement TCP/IP over carrier pigeons, or paper tape, or daemons summoned from the vasty deep.