We’ve never had guinea pigs or chinchillas, but we did have rats and they were wonderful pets–affectionate, smart, clean, and easy to care for. The only problem: whenever we turned out the lights to go to bed, the two rat sisters started fighting and you would hear thump-thump-thump-bump-SQUEEEAK! Turn the lights back on, and instantly they would be pretending nothing had happened. “I dunno, I didn’t hear no squeaking, did you hear a squeak? Look at us, we’re just sitting here nice and peaceful…” But they never did each other an injury, and the second time you turned the lights out, they’d behave themselves.
Warning: If you have a chinchilla who thinks he’s a cat, don’t let him near the toilet paper.