The presence of a YAFM in the source code of NetHack for eating a flint stone suggests that the DevTeam may have considered including the ability to eat stone at some point - this is considered a deferred feature, since it has yet to be implemented as of the latest stable version. SlashTHEM prints this message whenever you eat a non-cursed flint stone.
Lithivores can eat any items made of glass, mineral, bone or gemstone - this includes (but is not limited to) all gems, rocks and gray stones, as well as all potions, crysknives and mineral rings; eating a potion is the same as quaffing one in practice. These objects are also considered treats for pet lithivores. Polymorphing into a lithivore allows you to eat the same types of objects.
The following monsters are lithivores:
Rocks are by far the most common type of lithivorous 'food' a player will encounter, and make a plentiful source of nutrition for a pet lithivore - a single rock alone provides 250 points of nutrition. However, valuable tools such as unicorn horns, figurines and crystal balls can be eaten as well, so avoid leaving them around such monsters (particularly pets) if possible.
Players may also polymorph into lithivoric monsters such as xorns for relatively standard reasons such as eating jewelry, as well as somewhat more unorthodox uses - e.g., you can eat away an annoying loadstone weighing you down.
- You hear a grating sound.
- A monster is eating stone somewhere on this level.
- You ate a non-cursed flint stone while in the form of a lithivore; this exercises constitution.