Grue

Overview

The grue's introduction into the Zork series was started with the line in Zork I: "It is pitch black. You are likely to be eaten by a grue."  When the text : "What is a grue?" is entered the game responds: "The grue is a sinister, lurking presence in the dark places of the earth. Its favorite diet is adventurers, but its insatiable appetite is tempered by its fear of the light. No grue has ever been seen by the day, and few have survived its fearsome jaws to tell the tale.". Should the player continue to wander in the dark it is very likely that they will be eaten by a grue and the game will end.
 
One of the most notable things about grues was that nobody within the fiction had seen what a grue looked like and for a long time this remained a mystery, although an illustration of one did appear in a Zork gamebook and the game Wishbringer allowed players to discover a baby grue which was described as a "horrid little beast with red eyes and slavering fangs". Zork: The Undiscovered Underground had the player for the first time observe a grue and transform themselves into one. Grues appear to have a fish-mouthed head and fur all over, and are repeatedly referred to using phrases referencing razor-sharp claws, slavering fangs and horrible gurgling noises.
 
Grues were added to the Zork games as a way of forcing players to solve the light puzzles of the game before venturing through pitch black areas. Zork's predecessor Colossal Cave Adventure used bottomless pits in place of grues, however a different type of hazard had to be found for Zork as the alternative was using bottomless pits in places where it didn't make sense such as in areas with rooms below or on the ceiling. The Zork prequel Zork Zero revealed that the grues began wandering the dark areas of the world, searching the world for food when the game's protagonist used a magical device to fill in the bottomless pits of the world, chasing the grues out of their previous homes. The game Planetfall explains that grues were later taken from their home planet (presumably the planet Zork takes place on) by the spaceship in Starcross and ended up on Earth, then following humans across the galaxy and becoming a pest for humanity.
 
Despite the grues always appearing with an intolerance for light, exposure to light seems to affect them differently in different games. Some games seem to suggest that grues cannot be killed by light but feel great pain when exposed to it, however Zork: The Undiscovered Underground presents evidence that grues spontaneously combust when exposed to light sources. In Spellbreaker if a player shapeshifts into a grue and remains in the light for too long they will die, suggesting that grues probably do in some way perish when in light. A running joke within the Zork games are seeming means of protection against grues which don't actually work such as the grue repellent in Zork II.
 
In Sorcerer it is revealed near the end of the game that the villain is attempting to engineer a light-resistant grue and in Beyond Zork the primary antagonist is an 'Ur-grue', although the Ur-grue seems more like a dark god than a ferocious monster. It is also possible that the Ur-grue is the grue that created all other grues or all other grues originated from. In earlier Zork games players could only be eaten by a grue when moving, however in later games players could be eaten even when standing idle in pitch black areas.
 

Appearances Outside Infocom Games

Due to the popularity of Infocom's text adventure games and the influence they have had, particularly Zork, grues have become largely recognised among certain computer-using subcultures such as hacker and nerd cultures. A number of other games similar to Zork have also included grues such as Ancient Domains of Mystery. In the psychological thriller game Alan Wake when the protagonist turns off the lights in a cabin at one point the character Barry Wheeler says "Fine, I'll just sit here in the dark, maybe get eaten by a grue." 
 
They are the subject, along with Zork in general, of the song "It Is Pitch Dark" by MC Frontalot, who uses the line "You are likely to be eaten by a Grue." in the chorus.