Generally, do not read a cursed spellbook. Reading a cursed spellbook has one of several random effects, defined by the cursed_book function in spell.c. These effects can also happen when you read an uncursed spellbook which is too difficult for you, but blessed spellbooks never cause these bad effects.
Sometimes, "You feel a wrenching sensation" and teleports you. That is not so bad, but the other random effects are much worse. When you read a cursed spellbook, one of these happens at random:
- "You feel a wrenching sensation" and are teleported.
- "You feel threatened." The effect is to aggravate monster around you.
- You become blind for 100 to 250 turns.
- You lose all of your (visible) gold.
- You become confused for 7 to 16 turns. If you are already confused, you remain confused for 7 to 16 additional turns.
- It is a contact-poisoned spellbook, and you are poisoned, losing up to 4 points of strength and 10 points of health. A contact-poisoned spellbook can also corrode your gloves; or rather it could, if your gloves are gauntlets of power.
- "As you read the book, it radiates explosive energy in your face!" (Replace face with whichever body part you have while polymorphed.) You will lose up to 25 hp, but if you have magic resistance then you will avoid harm.
- The spellbook randomly curses some items in your inventory.
The above list is numbered to match the minimum spellbook level needed to reach that effect. For example, a cursed spellbook of level 3 might teleport you, aggravate nearby monsters, or blind you, but it will not take away your gold or poison you. The random curse will not happen, because there are no level 8 spellbooks.
In addition to the random effect chosen from above, you will be paralyzed for the same number of turns as were needed to (attempt to) read the book. [1]
Finally, you have a 1/3 chance of destroying the spellbook every time you attempt to read it (always if explosive energy effect).