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: