Cursed spellbook

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.

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:

1. "You feel a wretching sensation" and are teleported.
2. "You feel threatened." The effect is to aggravate monster around you.
3. You become blind for 100 to 250 turns.
4. You lose all of your (visible) gold.
5. You become confused for 7 to 16 turns. If you are already confused, you remain confused for 7 to 16 additional turns.
6. 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, except that there are no corrodeable gloves in vanilla NetHack.
7. "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.
8. 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 2 might teleport you, aggravate nearby monsters, or blind you, but it will not take away your gold. The random curse will not happen, because there are no level 8 spellbooks.