Cujo wasn't wagging his tail. The trained dog who was playing Cujo (whichever one was used in that scene, as there were 5 used throughout the movie) does not actually have rabies and is not a vicious dog. St. Bernards are big lovers, sweet dogs who enjoy being around people. You can train a movie dog to do a lot of things, but you can't train them not to wag their tails at the wrong time. That's just part of working with live animals.

I edited the post title. My mistake lol =P

He was like, U wanna get down punk!
Spoiler alert for them spoil sports out there! Y'all like spoiled milk, stop crying over it!

It's always so funny to me when someone puts "Spoilers" in the thread title, when the spoiler IS the thread title.
+1

It's always so funny to me when someone puts "Spoilers" in the thread title, when the spoiler IS the thread title.

Judging by his house and how he was living, I could understand Gary's thoughts about not caring. Cujo also wagged his tail right after he killed him, too.
The director may have left that in to show that C actually enjoyed it.