# Passive attack
Some monsters possess a passive attack - it is used automatically in retaliation to a melee attack against the monster.  They can be avoided by use of ranged weapons, pounding with a polearm or lance, or being resistant to the attack. Passive attacks are not affected by magic cancellation.
The most infamous example of such a passive attack is the floating eye's paralysis gaze - hitting a floating eye normally paralyses the player for a period of time, during which they are vulnerable to outside attack - a cause of numerous YASDs.  Other well-known examples include the various jellies, puddings, molds and acid blobs.
A passive attack is denoted by AT_NONE in the source code[1].

Contents

1 List of passive attacks

1.1 Acid
1.2 Stoning
1.3 Rust
1.4 Corrosion
1.5 Magic missile
1.6 Drain enchantment
1.7 Paralysis
1.8 Cold
1.9 Stunning
1.10 Fire
1.11 Electricity
1.12 Sticky
1.13 Slime

2 References

List of passive attacks
Passive attacks against the player are handled in uhitm.c:passive().  Monsters have at most 1 passive attack, which is defined separately from any other attacks they might have.

Acid
b&nbsp;acid blob, j&nbsp;spotted jelly, j&nbsp;ochre jelly, F&nbsp;green mold

50% chance of an acid damage.  If this succeeds, there's a 1/30 chance that your armor is subject to corrosion
1/6 chance, independent of the above, that whatever you attacked with (boot, weapon, etc) is subject to erosion
Your strength is abused
Stoning
c&nbsp;chickatrice, c&nbsp;cockatrice

If you hit with a bare appendage, you turn to stone and die instantly (unless stoning resistant)
Rust
R&nbsp;rust monster

If the monster is cancelled, nothing happens
If you kicked it, your boots suffer the effects of a rust trap
Otherwise, 1/6 chance that your weapon/gloves are subject to rust
Corrosion
P&nbsp;black pudding

Exactly like the rust attack above, but with the more-powerful corrosion effect
Magic missile
@&nbsp;Oracle (the source code comment is "wrath of gods for attacking Oracle")[2]

If you have magic resistance, no effect
Else, you are hit with a magic missile attack
Drain enchantment
R&nbsp;disenchanter

If the monster is canceled, nothing happens
If you attacked with an enchanted weapon/boots/gloves, they lose 1 enchantment.  Artifact weapons resist the drain 90% of the time, and ordinary equipment resists 10% of the time.
Paralysis
b&nbsp;gelatinous cube, e&nbsp;floating eye

If the monster is canceled or dies from the blow, nothing happens
If you have free action, "You momentarily stiffen"
If it is a floating eye and you have reflection, you cannot see it, or it is blind, nothing happens
Else, there is a 2/3 chance that you will be paralyzed
Being frozen by a gelatinous cube abuses dexterity
Cold
j&nbsp;blue jelly, F&nbsp;brown mold

If the monster is canceled or dies from the blow, or if you are cold resistant, nothing happens
Else, there is a 2/3 chance that you suffer a cold attack
The monster gains half its attack damage in HP, possibly increasing its max HP
If the monster's max HP is now high enough, it reproduces
The self-healing makes blue jellies especially deadly to lower-level characters who can't reliably hit hard enough to offset the healing.

Stunning
F&nbsp;yellow mold

If the monster is canceled or dies from the blow, nothing happens
2/3 chance that you become stunned
Fire
v&nbsp;fire vortex, E&nbsp;fire elemental, F&nbsp;red mold

If the monster is canceled or dies from the blow, or if you are fire resistant nothing happens
2/3 chance of fire damage
If you are polymorphed into an iron golem, you heal by the damage amount, instead
Electricity
v&nbsp;energy vortex

If the monster is canceled or dies from the blow, or if you are shock resistant nothing happens
2/3 chance of shock damage
If you are polymorphed into a flesh golem, you heal by 1/6 of the damage amount
Sticky
m&nbsp;large mimic, m&nbsp;giant mimic

If you walk into the mimic without knowing that there is a monster there, you are affected by their sticking attack, and cannot move away.
Slime
Although the green slime has a passive slime attack defined, there is no code to handle it.
References

↑ Monattk.h in NetHack 3.4.3, line 12

↑ uhitm.c in NetHack 3.4.3, line 2222

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