If you don't know what an Infocom-style grue is,
click here first and read.
I was thinking on it, and I've decided upon my own explanation as to why and how grues seemingly appear out of nowhere in any dark place (and how they instantly disappear when it's light again). They make some explanations in the Wikipedia article, but I wasn't satisfied, considering that 'shadow jumping' is a rather abstract concept not likely to recur often (let alone in the Zork universe), and I just don't think they use tunnels like that.
Anyway, the idea is that grues are actually always present—everywhere (even in the light)—but that they are only visible and substantial in the dark. Perhaps it's like darkness takes them into the adventurer's dimension; perhaps their dimension is always dark. Of course, this doesn't explain the exploding grue that was found in the light and such (but I think that wasn't an official game, anyway). Perhaps they have devices that enable them to come into the adventurers' universe, and the one that exploded had one that malfunctioned.
This idea would explain how grues always show up when it's dark—shadow jumping doesn't do that so much (the grues would probably need to have some knowledge about the place before shadow jumping to it).
Anyway, I'm imagining ideas for text adventures—I might implement this in one I make. I've been extending my Python text adventure model, lately—so that's what brought this up.
