In Of Mice and Men, what did Carlson do with his luger? Why?

Carlson shot Candy's dog with his luger.  The dog was not only old, blind, and could barely walk, but the men in the bunkhouse kept complaining about how badly the dog smelled.  While Candy realized that the dog was well beyond its prime and was barely existing, he didn't have the heart to put the dog out of its misery.  He'd raised it since it was a pup, and Candy could not bring himself to shoot it.  Even after Carlson suggested that shooting the dog in the back of the head would be the kindest way to put the dog down, Candy still refused to do it himself.  He did, however, allow Carlson to do the deed.  This event foreshadows when George is faced with the decision to shoot Lennie to protect him from Curley's wrath and/or the repercussions of the law for killing Curley's wife, even if it was an accident.