A pack rat is a rodent appearing only on the Rat King's level in SLASH'EM. It can steal items, but cannot teleport away like a nymph, but rather attempts to run away like a monkey. Fortunately it is not very dangerous, having the same level as a sewer rat (zero). It can be hard to distinguish the pack rats among all the other rats on the Rat King's level, particularly since the black rats which also appear there share the same glyph.
In real life
Pack rats in real life are not true rats; rather, they are rat-like rodents known for burrowing in attics and stealing small items, particularly shiny ones.
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."