Grue

You have been eaten by a grue.

The first mention of grues in the Zork games is the following ominous sentence:

It is pitch black. You are likely to be eaten by a grue.

Further investigation (by asking the game) will reveal more about their nature:

> what is a grue?

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 light. No grue has ever been seen by the light of day, and few have survived its fearsome jaws to tell the tale.