Diet
The diet of a monster describes which types of things it will eat.
Every monster, including yourself, is restricted to eating only certain materials. Solid foods that are edible to your starting character are generally classified as comestibles, but if you polymorph into a different type of monster, your new diet might include such things as shirts or wands. Independently of diet, you can also quaff any form of liquid nourishment, provided you are capable of drinking.
It is also helpful to be aware of the diets of your pets or potential pets you want to tame (that pony wants an apple, not a nasty tripe ration!) and of monsters that might go after your treasures (a rock mole ate my gold stash!). Monsters other than yourself decide whether to eat something according to their dietary preference and hunger, but will not eat harmful or inedible objects even when starving. No monster but you can open tins of food.
Note that being capable of eating something does not mean that you should eat it. Eating a dead cockatrice by mistake has ended many a game, and eating your own race carries the penalties of cannibalism. Monks suffer an alignment penalty for eating non-vegetarian food. Three conducts tracked by the game entail voluntarily restricting your diet: vegetarian, vegan, and foodless.
Internally, the diet of a monster type is indicated by the flags M1_CARNIVORE and M1_HERBIVORE; both flags are set for an omnivore, and neither is set for inediates and metallivores.
Omnivore
Most humanoid monsters, including yourself initially, are omnivores. This diet is essentially a combination of carnivore and herbivore.
Carnivore
Carnivores are monsters that (when tamed) prefer to eat meat. Tripe and meat created with stone to flesh are considered treats. They will eat any safe corpses and eggs that they find on the ground. They will eat "people food" such as food rations, pancakes, or fortune cookies if they are hungry and vegetarian food such as fruit and melons if starving. They will not eat vegan corpses such as mold or lichens, nor will they eat tins.
Herbivore
Herbivores are monsters that (when tamed) prefer to eat vegetable matter such as fruit, vegetables, fungi, and other plants. Apples and carrots are considered treats. They will eat safe vegan corpses such as lichens, mold, shriekers, blobs, and jellies if they find them lying on the ground. They will also eat melons, oranges, pears, wolfsbane, garlic, kelp fronds, and so on, but only when hungry. If they are very hungry, they will eat some people food like food rations, pancakes, and lembas. They will never eat meat products, meaty corpses, eggs, or tins.
Metallivore
Metallivores subsist on metals, including not only metallic weapons and armor but also rings, amulets, and wands made of metal. In fact, a useful strategy is to polymorph into a metallivore in order to gain intrinsics by eating jewelry. They also eat tins of food, biting right through the tasty metal. Non-rustproof iron objects are considered treats. Unlike xorns and rock moles, rust monsters are restricted to the one metal that can rust, iron.
Inediate
Inediates do not need to eat any kind of food to stay alive. Generally, monsters that are undead, demonic, angelic, or otherwise magical in nature are inediate, but there are exceptions, such as ghouls.
Special cases
Several monsters have unique diets.
- Gelatinous cubes eat any organic material (anything that can rot), and engulf most everything else.
- Umber hulks eat rock.
- Ghouls eat only "old" corpses.
- Mind flayers eat the brains out of living monsters.
