I spent time in the Rat Lab at UCSB many years ago. Where the rats lived was a windowless room with an day/night cycle on a timer. If you were in there when the lights went out, the rats—hundreds of them—seem to come to life. Very strange, almost nightmarish experience.
I have worked with rats, too. They were not as docile as mice. I didn’t like going to the room where they were kept. The mice never bothered me.