If you wield the artifact weapon named Sting, then you are warned of orcs. You can detect the locations and types of all orcs on the current dungeon level, as if you could see them. This applies to any monster of orcish race, including any 'o' monsters and also orc mummy and orc zombie. In SLASH'EM, certain roles are warned of undead. This is an innate property of an Undead Slayer from experience level 1, or a Necromancer from level 3. It detects the locations of all undead monsters on the current level.