Like a lot of folks, I was bothered by Luke's insistence that there was still good in Vader and his efforts to save him in RotJ. And while I could articulate many of my reasons, I still felt that there was something more that I just couldn't quite put my finger on. Today, at work, a coworker was tugging a rack behind her on a hand dolly and I said, "Hyah, mule! Hyah! Hyah!" She flashed a grin and then quickly adopted an expression and posture which reminded me of the Grinch's dog, Max. I laughed and thought to myself, "Of course, we knew that the Grinch was worthy of redemption because he had a dog." And that's when it hit me. The most common trope in movies and TV is that the most irredeemable villains, if they have a pet, it's a cat. Because cats pretty much don't give a shit. Dogs, OTOH, are portrayed as being able to know if someone is decent or not (think about the use of dogs in the first Terminator movie). So, it seems to me that if Vader had had whatever the Star Wars universe version of a dog is, as his pet, it would have made his conversion to the Light Side of the Force at the end of RotJ more believable.