What did Carlson do with his Luger. Why?

Carlson shot Candy's dog. He thought the dog useless, stinky, and old..... he considered himself to be doing the dog a favor.

He drug Candy's blind and nearly deaf dog out of the room and put him out of it's misery. This made Candy depressed for a few pages but he slowly forgot about it and began talking with the others again.