The Rat is an enemy in Duke Nukem Forever.
The Rat is the smallest enemy encountered in DNF and only attacks Duke when he's shrunk down in size during certain levels. In all other levels, they are harmless but Duke can pick them up, place them in a microwave, throw, or squeeze them to death. They also come in brown, gray, and maybe a few other colors.
The Rat's only form of attack is biting up close. It has small amount of health (probably smallest compared to all the enemies in DNF) and hence is easily killed.
In Duke Nukem 3D, rats could be seen scurrying around on the ground, particularly in air vents and in sewers, but were not enemies.
Rats pose no threat when in normal size.
While shrunk, rats will frequently attack first and deal moderate damage. They can be easily killed, but will swarm if given the chance.