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."
[ 1984, by George Orwell ]