The floating eye is extremely slow and does not attack, but each time it is attacked in melee there is a 2⁄3 chance of it using a passive paralyzing gaze attack that immobilizes the attacker, unless that attack kills the floating eye. If you are paralyzed by a floating eye, the length of time you are immobilized depends on your Wisdom and the floating eye's level - if your wisdom is 12 or lower, there is a 1⁄4 chance of being paralyzed for exactly 127 turns; otherwise, the duration (lvl + 1)d70 turns. Floating eyes are the indirect cause of many YASDs this way.
Only 50% of floating eyes will leave a corpse upon death.
As indicated above, and in-game via the encyclopedia entry, the floating eye is dangerous to attack in melee, but its gaze will not trigger if attacked outside of melee range. Additionally, it does not occur if the floating eye has been cancelled or blinded; note that there is a 1⁄500 chance that you will lose one point of Luck if you attack a blind floating eye. A source of reflection or free action will completely prevent paralysis; hallucination will cause you to ignore the passive gaze 3⁄4 of the time. While you can apply a mirror to paralyze a floating eye, this does not prevent its passive gaze from paralyzing you.
Any ranged attacks - daggers, polearms, spells, etc. - can safely dispose of floating eyes, and even throwing junk weapons or rocks will suffice. If fighting one inside a room, you can wait for it to move so that you can retrieve your thrown weapons if desired. Alternately, you can blind yourself by applying an appropriate item, such as a blindfold, towel or a cream pie - as long as you cannot see the floating eye, you can attack it without consequence. Another option is to make the floating eye invisible, e.g. with a wand of make invisible (unless you have the see invisible intrinsic).
If you are facing a floating eye in a corridor without any means of ranged attack, and wasting turns is not an issue, you can place yourself between the floating eye and an obstacle of some sort (such as a locked door, boulder, or passive creature) so the paralysis will cause no lasting damage other than wasting turns; however, you will then likely have to contend with hunger instead.
Pets will not attack floating eyes in melee most of the time; a leather drum can unfreeze a pet that is paralyzed as a result of attacking one.
Floating eyes are a commonly sought out source of telepathy - many players make and/or seek out tins of floating eye meat as a means of re-gaining telepathy if is lost later on (e.g. through an accidental murder). Zen players usually have the explicit goal of finding and killing a floating eye in order to eat it and make navigation safer, as most of the dungeon's inhabitants will become visible to them. Monks may be tempted to break the vegan/vegetarian conducts by eating one, though they can gain the comparable warning intrinsic by reaching experience level 7, and it is possible to receive telepathy as a boon from your god via prayer.
The floating eye has been present in the game since PDP-11, a variant of Jay Fenlason's Hack. It was also one of many monsters featured in pre-5.3 versions of Rogue, before it was replaced with the ice monster (seemingly due to copyright issues involving Dungeons & Dragons).
The floating eye may have been inspired by a similarly-named monster in the 1st Edition Monster Manual of Advanced Dungeons & Dragons. The floating eyes of AD&D are portrayed as an unusual type of saltwater fish, possessing transparent bodies and a single large eye with a three-inch diameter. Any creature gazing at it must make a saving throw versus paralysis, and failing results in being hypnotized into remaining stationary, usually leaving them at the mercy of any nearby predators; this is very similar to the gaze employed by the floating eye of NetHack, though AD&D floating eyes are not restricted to passive behavior.
In NetHack brass, floating eyes can additionally freeze attackers using polearms against them.
In dNetHack, the duration of the paralysis effect is shortened to 2d6 turns, making them less dangerous to melee. However, it is still safest to attack them at range, as 12 turns is still enough time for other monsters to appear and kill a character.
In FIQHack, floating eyes instead have an area-of-effect slowing attack; hitting one in melee no longer paralyzes you, but instead has a harsher passive slowing effect which will typically last well after you leave the former attack's area of effect and/or killing the floating eye.
Ravens will attack floating eyes as part of FIQHack's modified grudge system.
In NetHack 4, it is impossible to attack a floating eye in melee without being protected from its gaze in some way; monsters can still attack floating eyes normally and suffer paralysis. This was implemented to prevent aggravating deaths from early-game movement mistakes, as an accidental button press would often mean instant death.
In xNetHack, floating eyes are given a more visible glyph, e.
Floating eyes, not surprisingly, are large, floating eyeballs which drift about the dungeon. Though not dangerous in and of themselves, their power to paralyse those who gaze at their large eye in combat is widely feared. Many are the tales of those who struck a floating eye, were paralysed by its mystic powers, and then nibbled to death by some other creature that lurked around nearby.