5. Going into Hiding/ Becoming Quiet: If your normally social pet begins seeking more quiet time or begins sleeping a lot more, this can be a red flag indicating some form of pain or infection. This is a big one and you'll want to begin paying careful attention to see if you can uncover any other changes so that you can report these to the vet as well. In fact, one cat who recently swallowed a long piece of string that was constricting his intestines was simply noted to be sitting quietly and not bouncing around as he usually does. This change had only begun that morning, but his eyes seemed to say, something is wrong, and fortunately his very astute guardian rushed him to the vet where an x-ray revealed the foreign body and emergency surgery saved his life.