The logical thing to type when Infocom's Zork would warn you against being eaten by a grue. Doing so would prompt the game to explain what the hell a grue was. Now if I remember correctly, for a long time you could ask this of ANY Infocom game and it would still tell you, regardless of whether the game contained grues or not. For some reason my friends and I thought that was really cool.

Of course, back in the day, a game that allowed us to manipulate a little square carrying a big arrow for a sword which it used to kill ducks totally impressed us.