Amazon.com description: Product Description: What are InvisiClues? The essence of all Infocom interactive fiction is solving problems. The purpose of InvisiClues hint booklets is to maximize your enjoyment of the game by giving you only those hints that you need to continue playing and complete the game. The invisible hints generally progress from a gentle nudge in the right direction to a full answer. The questions, which naturally have to be visible, have been worded to give away as little as possible. You should not use the presence or absence of a question on a certain topic as an indication of importance, and you should not assume that long answers are associated with important questions. This booklet includes dummy questions and answers in order to minimize this problem. If you are stuck at some point in ZORK I, find the question that most pertains to your problem. Uncap the marker and run it once over the first hint. The writing will appear within a second or two. If you are still stumped, go on to the next hint. (Remember to recap the marker when you are done to prevent it from drying out. And by the way, these books are not immortal. InvisiClues you've developed will start to fade after six months). You can use the listing of how all the points are scored as a last resort. Once you have finished ZORK I, try the things in the "For Your Amusement" section. Don't look at them before you've finished. though - they may reveal the answers to certain problems.