Once upon a time my sister gave us a pair of white rats for Christmas. They were tame, affectionate, playful… with us humans.
But when it was bed-time and we turned out the lights, we would hear, coming from the rats’ aquarium, thump-thump-thump-thud-SQUEEEEEAK! And I’d turn the light back on, only to find the two little characters innocently sitting in the cedar shavings… as if to say “Fight? What fight? Who’s fightin’? We don’t know what you’re talking about, boss.”
At least they never hurt each other.