Blindness is an inability to see. When blind, normal movement will result in you using your hands to feel for items on the ground. Unseen items generally only appear as their object class, without even randomized appearance - for example, you will only feel "a wand" or "a potion". Items seen prior to blinding will continue to be identified with their randomized appearance.
The zen unofficial conduct consists of playing the entire game blinded.
If you move normally while blind, you will attack anything represented by I (or warning symbol) you walk into, as if it were invisible. Also, moving onto a seemingly empty square with a monster on it, will cost you a move (without attacking), show the monster as I and anger it if peaceful. This makes it very dangerous to move around while blind, because you could inadvertently kill your pet or anger a shopkeeper.
To partially avoid this, be sure to move with m followed by a direction. This causes you to move without feeling on the ground for items and generally without attacking monsters. But this still angers any peacefuls you bump into that weren't already shown in any way. If a stethoscope is only used once per turn, it can determine if there is something in the way without giving that monster a chance to move, since the stethoscope can be applied for free once per turn. If you are fairly confident that there are no monsters on the level that could seriously damage you in one hit, you could also wait for them to attack you first. Although if the monsters are faster than you, they can attack you and move away before you having a chance to react to the I that you discovered when they attacked you. In rare cases, #chatting is useful to test for non-silent monsters since it does not use a turn if you get no answer.
Monsters seen via telepathy or monster detection are handled normally, both moving normally and with m. You always attack warning symbols, unless you are m-moving into one that covers an I. Beware that even telepathy and warning put together don't show all types of monsters. (Further corner cases stem from hiders, mimics, Stormbringer, F, and deactivating safe_pet.)
Special care should be taken on levels with cockatrices on them. If there is a cockatrice corpse and you move around normally while blind, you may stumble on to the corpse and feel for it. If your character is not wearing gloves, this will result in instant stoning. Use the m movement prefix (as above) to avoid touching the corpse while moving. Additionally, if you try to : (look) or , (pick up) on a square with a cockatrice corpse while blind you feel the square and will also be stoned! Even worse, if you are blind and warned, moving with m into a cockatrice without a wielding anything or wearing gloves will still stone you in some cases: namely whenever the warning symbol does not cover an undisplayed I.
- Pardon me, foo.
- You moved with m into a pet either displayed as I or properly seen.
- You move right into foo.
- You moved with m into a non-tame monster either displayed I or properly seen.
- Wait! There's something there you can't see!
- You moved onto a seemingly empty square. Does not attack, but does anger peacefuls.
If you have telepathy, though, blindness can be quite useful as it enables you to see all monsters with brains on the level. Intrinsic telepathy is only active when you are blind; extrinsic telepathy will work like intrinsic telepathy when you are blind.
Ways to be blinded
In addition to this list, most of the methods to blind monsters also work on yourself.
- Drink a potion of blindness; this is not recommended
- Wear a blindfold or a towel
- Be attacked by a yellow light (preventable by wearing a blindfold or towel)
- Be attacked by a raven (preventable by wearing a blindfold, towel, visored helmet or lenses)
- Eat rotten food (one possible outcome)
- Be hit by a wielded or thrown cream pie (you can also apply one to yourself to cause the same effect)
- Apply an expensive camera at yourself
- Be zapped by (a wand of) lightning
- Engraving with a wand of lightning, unless you cancel at the prompt what text to engrave
- Be hit by the monster spells Blind or (as of NetHack 3.6.0) Lightning
- Apply a cursed towel (one possible outcome)
- Be hit by blinding venom
- Polymorph into a creature that has no eyes
- Read a cursed or difficult spellbook
- Apply a cursed unicorn horn (one outcome, not recommended)
- Be inside a gas cloud
A blind enemy will move and attack erratically, suffer a to-hit penalty and generally be much less dangerous, especially if you can keep moving. There are six main ways to inflict blindness.
- Apply an expensive camera. The tourist relies on this to survive early levels. Other adventurers tend to find them in the Gnomish Mines, where they may appear either in a cavern level or the Minetown hardware store. This will also cause enemies to flee.
- Throw a potion of blindness. This effect is much briefer than when quaffing.
- Zap a wand of lightning. Blinding is a secondary effect.
- Break (apply) a wand of light. This will also cause enemies to flee.
- Throw a cream pie. A run in with Keystone Kops allows you to really stock up.
- Polymorph yourself or your pet into a creature with a blinding attack.
Beware, blinded creatures do not respect Elbereth.
There are a few ways to cure intrinsic blindness - that is, blindness not from being blindfolded, cream pies, venom or applying cursed towels.
- You can wait for it to heal - this can take a few turns if the blindness was caused by eating rotten food or being hit by a potion of blindness, but will take many hundreds of turns if you quaffed a potion of blindness. Having read cursed/difficult spellbook takes quite a bit of turns too. If you do have to wait it out, make sure you have a good amount of food.
- Apply a unicorn horn
- Invoke the Staff of Aesculapius
- Eat a carrot.
- Cast a spell of cure blindness or extra healing.
- Drink a potion of extra healing, potion of full healing or non-cursed potion of healing.
- Praying to your god may help, but be aware that blindness is only considered a minor problem.
- Astral vision does not cure blindness, but allows you to see despite it.
Otherwise, you can remove whatever it is that is blindfolding you. Having a cursed blindfold or towel stuck to your face is considered a major problem, so if it is safe to pray, your god is likely to help you out of this predicament.
A few items allow you to resist blindness. While this can be useful in the early game, you usually have a unicorn horn by the time you have one of these (except for the potion of blindness, which is probably a bug).
The Eyes of the Overworld will not prevent blinding, but you will still be able to see while wearing them.
Until you have seen them, objects show up only as "a potion", "a ring", "a long sword" etc. A gray stones or rock is a "stone", glass or gem is a "gem". Only amulets and food are treated as seen.
You cannot class-name such objects, and any individual name will not be displayed (but will affect stacking and artifact naming). You can dip items in holy/unholy water when blind, thus "a cursed scroll". Poisoning and erosion status is shown. Dilution is only displayed if you know the appearance. Erodeproofing and charges are only shown if formally identified (even if you erodeproofed it yourself while blind).
A full list of ways to make an object "seen" while still being blind, e.g. for zen conduct:
- Formal identification from a scroll, throne, or spell. Also, your quest leader will identify your own quest artifact and the real Amulet of Yendor.
- A blessed potion of object detection makes the appearance of all objects on the current dungeon level known. This includes your and monsters' inventories, buried objects, and recursively the contents of containers.
- Buying or selling something at a shop. Contents of containers, stolen merchandise, and items covered by your credit when you teleport out are not made known.
- A wand of probing non-recursively makes any objects it is zapped at, containers' contents, and monsters' possessions seen. You can zap yourself.
- The appearance of your and your pet's starting inventories
- Eating one of a stack will make the remaining tins "seen".
- Eggs laid by you
- The special attacks of the Tsurugi of Muramasa and Vorpal Blade always tell you the artifacts's appearance. The gift you would receive on crowning as neutral or chaotic are made "seen" if you are already holding it.
- Viewing an item through astral vision.
You hear the appearance of a scroll a monster is reading, so you can name another one later. Since you cannot generally "see" the result of the scroll directly, scrolls will not usually auto-identify. The same is true for potions, you will hear the potion being quaffed, but will not see the result.
It is worthwhile considering the internals of blindness, which are quite complex, but their details shed light on the actions and exceptions described above.
The source recognises three forms of blindness:
"Blinded" refers to all forms of blindness that are intrinsic; that is, you would be blind if you were not wearing or wielding anything and polymorphed into a monster form with eyes.
The number of turns for which you are blinded is recorded.
Being "creamed" means you have a substance over your eyes physically restricting your vision. It is a subset of being "blinded", and stacks with blindness.
The number of turns you are creamed is recorded. It is always less than or equal to the number of turns you are blinded.
Items causing or curing creaming affect both the number of turns creamed and blinded by the same amount.
Actions that cream are:
- Being hit by, or applying a cream pie
- Being hit by blinding venom
- Applying a cursed towel
Actions that cure creaming are:
- wiping your face
- Applying a noncursed towel
All other actions and cures affect blindness only if it cures either, except prayer, which will cure both creaming and blinding.
The "creamed" status times out first. To understand how this works, consider the following hypothetical scenario wherein you are blinded for 100 turns. After 50 turns have elapsed, you will still be blind for 50 more turns. If, however, on that turn, you become creamed for a duration of 20 turns, you will be blinded for a total of 70 more turns - the first 20 of which you are considered creamed.
"Blind" means you currently cannot see. You can be "blind" without being "blinded", if your eyes are covered by a blindfold or a towel, or you polymorph into a monster with no eyes. You can be "blinded" without being "blind" if you have astral vision.
- src/hack.c in NetHack 3.6.0, line 1409
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- object_detect in detect.c in NetHack 3.6.0
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- src/u_init.c in NetHack 3.6.0, line 1074
- src/dog.c in NetHack 3.6.0, line 193
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