In Of Mice and Men, what is Carlson’s problem and what does he tell Candy to do?

In John Steinbeck's Of Mice and Men, Carlson cannot stand the smell of Candy's old dog. Carlson rants about Candy's dog soon after George and Lennie meet him:

"That dog of Candy's is so God damn old he can't hardly walk. Stinks like hell, too. Ever' time he comes into the bunkhouse I can smell him for two, three days."

Eventually, Slim, after being pushed by Carlson, convinces Candy to let him shoot his dog telling him the the "dog ain't no good to himself." Candy submits after protesting that he's "had 'im too long" and that he "don't mind takin' care of him."

This scene with the dog foreshadows George's eventual decision to shoot Lennie in the back of the head, like Carlson says Candy needs to do to the dog. This novela's primary theme concerns the exploration of the loneliness the characters suffer from on this ranch during the Great Depression. Steinbeck uses this theme to parallel the companionship Candy has with his dog to the one George and Lennie enjoy, which is such an oddity that the ranch's boss makes mention of it during their interview.

While Carlson might be guilty of not being tactful and from a certain selfishness, his suggestion that Candy shoot his dog might be correct to save the dog from suffering anymore. This parallels George's decision to shoot Lennie after he accidentally kills Curley's wife considering Curley had planned on making Lennie suffer by lynching him.