# Hallucination
In NetHack, hallucination is a status-impairing property that will cause you to perceive objects and monsters in a distorted fashion. Hallucination shows up on the status line as "Hallu".

Contents

1 Description
2 Sources

2.1 Cures

3 Strategy

3.1 Identifying items and monsters

4 History
5 Messages
6 Variants

6.1 SLASH'EM
6.2 GruntHack
6.3 dNetHack
6.4 EvilHack

7 References

Description
While hallucinating, object glyphs will be seen as continually changing items of the same class - a pick-axe may be seen as a sack or dagger, but not as a monster. This also applies to items in your inventory or on your square, but the actual appearance of those items will be accurately reported. Monsters themselves will cycle through various appearances, and whether or not they are hostile is obscured; monsters cannot be named while hallucinating. This perception changes every time the screen is updated, so even selecting an object or monster and pressing ; to see what it is appearing as will change it to something else. Hallucination abuses wisdom every 5 turns for its duration.
The set of names chosen for monsters while hallucinating includes a selection of various names from popular culture and entertainment, e.g. Barney the Dinosaur, King Kong, the Luggage, the Mother-in-Law, and The Ravenous Bugblatter Beast of Traal among others. The same applies for any mention of gold or zorkmids; similarly, hallucination replaces various standard messages with funny ones, such as "You hear the studio audience applaud!" and "You are getting the munchies".
Monsters cannot hallucinate, and anything that would inflict hallucination upon you will leave a monster confused instead.[1]
Hallucination has a few strange qualities as well: if you are hallucinating and targeted by the touch of death monster spell, instead of dying you "have an out of body experience". Note that this does not protect against Death's special deadly touch attack. Hallucination also has a 3⁄4 chance of protecting you from any gaze attack, including the floating eye's paralyzing passive attack.[2][3]

Sources
There are several means to induce hallucination:

Eat the corpse or tin of a yellow mold, violet fungus or any monster with a stunning attack. This lasts 200 (more) turns.[4]
Be hit by the exploding attack of a black light while not blinded.  This lasts 10d12 (more) turns.[5][6]
Quaff a potion of hallucination. This lasts 300–499 (more) turns for a blessed potion, 600–799 (more) turns for an uncursed one, and 900–1099 (more) turns for a cursed potion.[7]
Apply a crystal ball and fail the intelligence check, which has a 1⁄5 chance of "[zapping] your mind" and causing hallucination for 1–100 (more) turns.[8]
Apply a cursed unicorn horn, which has a 2⁄13 chance of inducing hallucination. This lasts 10–99 (more) turns.[9]
Trigger a container trap, which has a 3⁄26 chance of producing a "cloud of 

<random color=""> gas" (unless the container trap is harmless). This causes hallucination for 16–20 (more) turns, and also stuns you for 16–22 turns.[10]
Cures
Hallucination can be cured by:

Applying a noncursed unicorn horn
Quaffing a potion of sickness, extra healing, or full healing
Prayer - hallucination is considered a minor problem
Waiting for the effect to end on its own
Additionally, obtaining a source of hallucination resistance will suppress the effect for its duration. Currently, the only means of doing so is to wield Grayswandir.

Strategy
Hallucination can be both funny and dangerous - as indicated previously, inability to distinguish a peaceful monster from a hostile one can quickly prove fatal. It is an easy and somewhat common mistake to lose track of which monster is your pet in a melee situation and accidentally kill it. You will also be unable to distinguish one hostile monster from another, making it difficult to prioritize targets. Additionally, engraving while hallucinating has a high chance to fail.
If you have quaffed a potion of hallucination and have no way to cure yourself, it is wise to keep away from your pet and/or large concentrations of peaceful monsters for the duration - areas such as Minetown (and the rest of the Gnomish Mines if dwarves and/or gnomes are peaceful towards you) are made rife with peril.
Once you have a noncursed unicorn horn, hallucination is trivial to cure. Until then, you can avoid most causes of hallucination somewhat easily, with the exception of the typically-invisible black light. If you are aware of the light's approach (e.g. through see invisible, monster detection or noticing your pet fighting something invisible), you can blindfold yourself so that the explosion has no effect. Failing that, hallucination from a black light only lasts for around 100 turns at most, so you can shut yourself in a room and wait it out.

Identifying items and monsters
It is a Bad Idea to eat an unidentified tin while hallucinating. Your perception of the smell will be affected, and you might eat meat of your race without realizing it. Spinach is still identified normally (except to distort the color of cursed spinach), and cockatrice meat always "smells like chicken" when hallucinating[11] - all other contents cannot be readily distinguished until the tin is eaten, or else identified beforehand. You may also wish to refrain from quaffing unidentified potions until you recover from hallucination.
When monsters are nearby, you can still #chat to a hallucinatory monster to potentially identify it by its response - e.g., your pet little dog will yip or bark, regardless of whether it appears as a lichen or Archon. Thus, it can be useful to determine if a monster is tame or peaceful before attacking. A stethoscope will also correctly identify a monster's attributes while misidentifying the monster itself. If you kill a hallucinogen-distorted monster and step onto the square containing its corpse, the corpse will be accurately identified. 

History
Hallucination's effect on gaze attacks was introduced in NetHack 3.6.0.

Messages
Oh wow! Everything <looks feels=""> so cosmic!
You are hallucinating - "feels" is used if you are also blind at the time.
Oh wow! Great stuff!
You ate the corpse or tin of a monster and began hallucinating.
You have a peculiar feeling for a moment, then it passes.
You quaffed a potion of hallucination while you had hallucination resistance - the hallucination is applied and immediately suppressed by the property.
Far out! Everything is all cosmic again!
You were blind, and either recovered or removed what was covering your eyes while hallucinating.
Everything <looks feels=""> SO boring now.
You are no longer hallucinating - as with the first message, "feels" only occurs if you are also blind.
Your vision seems to flatten for a moment, but is normal now.
As above, but you had a source of hallucination resistance when it wore off.
Variants
SLASH'EM
In SLASH'EM and its variants, hallucination also distorts items you are standing on as well as your inventory, which makes it a far more hazardous ailment; additionally, you cannot name specific objects or object types until the effect wears off. In addition to the usual sources, eating a mushroom or a pink pill may also cause hallucination, and applying a medical kit can cure it. However, your deity will still consider it a minor problem for purposes of prayer.
Avoid quaffing a potion of hallucination without a remedy on hand such as a unicorn horn, set to an inventory letter that you can remember. Hallucination can be moderately useful as a way to bless items without breaking atheist conduct: asking a shopkeeper to uncurse an item while hallucinating has a chance to bless it instead.

GruntHack
In GruntHack, hallucination causes the walls and floor of the dungeon to oscillate through a rainbow of colors each time the screen updates. As in SLASH'EM, it obscures the appearances of monsters, as well as items on the ground and in your inventory, and additionally hides object types. The intensity of the effect depends on the length of time you are hallucinating for, and will gradually affect fewer items and monsters as it comes closer to wearing off.

dNetHack
In dNetHack, hallucination affects object appearances as well as monsters; while your inventory is not affected, this does include prompts for looting containers with items and picking up multiple items from one square.
Hallucinating while eating a corpse that grants telepathy adds a point of insight, while quaffing a cursed potion of hallucination reduces your insight by one point. As with SLASH'EM, requesting the item-uncursing service while hallucinating may also cause the item to be blessed instead.

EvilHack
In EvilHack, intelligent monsters can generate with a potion of hallucination as an offensive item, and will throw it at you accordingly.

References

↑ src/mhitm.c in NetHack 3.6.0, line 1088

↑ src/mhitu.c in NetHack 3.6.0, line 1990

↑ src/uhitm.c in NetHack 3.6.0, line 2421

↑ src/eat.c in NetHack 3.6.6, line 1110

↑ src/monst.c in NetHack 3.6.6, line 965

↑ src/mhitu.c in NetHack 3.6.6, line 2122

↑ src/potion.c in NetHack 3.6.6, line 639

↑ src/detect.c in NetHack 3.6.6, line 1129

↑ src/apply.c in NetHack 3.6.6, line 1942

↑ src/trap.c in NetHack 3.6.6, line 4970

↑ src/eat.c in NetHack 3.6.0, line 1619

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