:I opened the lid to my black rat's feeding container today (he's about 6 months old), and I guess it spooked him because he started shaking his tail rapidly. Of course on the newspaper lining, it sounded just like a rattlesnake. Is this common?
Its perfectly normal...I have had all sorts of different type of snakes do that. Its a warning for preditors to stay back. Not that they are always trying to sound like a "rattle snake" but a warning just of a rattling sound.