grue

grue
 n.

   [from archaic English verb for shudder, as with fear] The grue was
   originated in the game {Zork} (Dave Lebling took the name from Jack
   Vance's Dying Earth fantasies) and used in several other {Infocom}
   games as a hint that you should perhaps look for a lamp, torch or some
   type of light source. Wandering into a dark area would cause the game
   to prompt you, "It is very dark. If you continue you are likely to be
   eaten by a grue." If you failed to locate a light source within the
   next couple of moves this would indeed be the case.

   The grue, according to scholars of the Great Underground Empire, is a
   sinister, lurking presence in the dark places of the earth. Its
   favorite diet is either adventurers or enchanters, but its insatiable
   appetite is tempered by its extreme fear of light. No grues have ever
   been seen by the light of day, and only a few have been observed in
   their underground lairs. Of those who have seen grues, few have
   survived their fearsome jaws to tell the tale. Grues have sickly
   glowing fur, fish-mouthed faces, sharp claws and fangs, and an
   uncontrollable tendency to slaver and gurgle. They are certainly the
   most evil-tempered of all creatures; to say they are touchy is a
   dangerous understatement. "Sour as a grue" is a common expression,
   even among grues themselves.

   All this folklore is widely known among hackers.