I don't think it's any of these things. I think for most people, it's just difficult to know when to stop treatment and when the animal is "ready" to go. I've had several rats die, but usually I only have an indication that they're sick a few days before they die. My last one, however, had a tumor. I knew that eventually her quality of life would no longer be there and that I'd have to have her PTS. For weeks I'd spend time with her, and besides the tumor I'd've had no idea that she was sick, she was her same chipper self. Unfortunately I was out of town when she took a turn for the worse, and my roommate who was taking care of her probably watched her suffer for a few days. As soon as I got back I knew it was time, but it was still an extremely difficult decision.... her death hurt me more than any other of my rats' deaths, I guess because I felt much more responsible for her death. I still question whether I should have had her put to sleep when I first noticed the tumor, instead of letting her live with it the last few weeks of her life. There was nothing that could be done about it, and I knew it would eventually get to the point where she'd be PTS.... so should I have done it in the beginning??