Rats are long-tailed rodents, the three in the family being sewer rats, giant rats, and rabid rats. They are generally encountered in the early part of the dungeon. Their lycanthrope relative, the wererat, can summon an entourage of these creatures as allies.
A giant rat has slightly more health and nutritional value than its sewer rat brethren, but it moves more slowly.
A rabid rat is the most dangerous member of the rat family in NetHack. It has a special constitution-draining poisonous bite, which has a slim chance of causing instadeath if not poison resistant. This bite can be protected against with high magic cancellation. Its corpse is poisonous, but will not grant poison resistance.
Rats are long-tailed rodents. They are aggressive,
omnivorous, and adaptable, often carrying diseases.
"The rat," said O'Brien, still addressing his invisible
audience, "although a rodent, is carnivorous. You are aware
of that. You will have heard of the things that happen in
the poor quarters of this town. In some streets a woman dare
not leave her baby alone in the house, even for five minutes.
The rats are certain to attack it. Within quite a small time
they will strip it to the bones. They also attack sick or
dying people. They show astonishing intelligence in knowing
when a human being is helpless."
Convicts begin with a pet sewer rat and have a chance of taming or at least pacifying hostile rats by #chatting with them.
In the Convict patch and most variants that incorporate it, giant rats grow up into enormous rats.
The development version of UnNetHack removes the enormous rat, so giant rats grow up directly into rodents of unusual size.
To set certain popular misconceptions to rest once and for all:
1) He was not found wandering the sewers of London as a child during
the winter of 1864, unable to say anything more than "Powerful
big rats, gentlemen."
2) He was never exhibited in public houses to the curious; only
briefly in July, 1865, to selected gentlemen of standing from
the scientific and literary community.
3) He did not have a vestigial tail.
4) He did indeed have what most people would commonly understand
5) He was not actually the pilot of the Zeppelin, although he did
disappear for good following the explosion.
6) There is obviously no "underground kingdom beneath London,
inhabited by huge, intelligent rodents." And even if there were,
and suggestion of Neil's involvement in the mazy territorial
negotiations between Londons Above and Below can be considered a
joke, and in poor taste at that.
7) He was afraid of neither mirrors nor street conjurers.
8) There were no tooth marks on the bones.
Rodent of unusual size
Rodents of unusual size (R. o. U. S.) are the strongest rats in the Convict patch and variants that include it.
Enormous rats grow up into R. o. U. S., except in the development version of UnNetHack, where enormous rats are removed and giant rats grow up into R. o. U. S. instead.
"Rodents Of Unusual Size? I don't think they exist."
This page is based on a spoiler by J. Ali Harlow.