George is concerned about the presence of the yellow box of insecticide near the place where his bunk is supposed to be. Thus, to alleviate George's concerns Candy seems to concoct an excuse and goes into great detail about the cleanliness of the bunk's previous occupant, who was a blacksmith (probably not the cleanest occupation on the planet).
Part of Candy's logic is interesting. One of the reasons George should not be worried about the cleanliness of the bed is because the previous occupant was a "nice fella." Of course, Candy seems to think that just about everyone is a "nice fella." Even after Lennie kills Curley's wife, Candy has a hard time believing that "such a nice fella" could do something like that. As Candy's name implies, he always seems to have something nice to say about everyone.
Despite Candy's making excruciating an excruciating effort to convince George that the bunk is clean, George remains skeptical ("I ain't so sure," said George skeptically." Eventually, though, George accepts the bunk.
Steinbeck was trying to create a picture of the hard lives of itinerant farm workers. George's reaction to the bug killer helps to show that there are many such bunk houses in California and that living conditions can be bad. George has had plenty of experience. He inspects the assigned bunk before he accepts it. It would be natural to assume that a bunk that has been slept in by many different hobo-type men might not be too clean. George seems particularly concerned about what he calls "pants rabbits" and "graybacks." Evidently these are both slang terms for crab lice. This suggests that bunks all over California might be infested with these lice as well as with bedbugs.
Candy makes a strong effort to convince George that the bunk is clean because it is Candy's job to keep the bunkhouse clean. Candy is terribly afraid of losing his job--and it wouldn't take much of an excuse for the boss to fire him. A man with only one hand cannot be a very efficient housekeeper. This episode characterizes Candy as a desperate old man at the same time it characterizes George as a foxy and feisty individual who hates the kind of life he has to lead. Candy may be lying about the "blacksmith" who left the yellow can behind, but he is probably telling the truth when he says that he "Finally quit about the food."
Steinbeck does not describe the room where the men all eat or the kind of food they get. But the reader can get the impression from the blacksmith's opinion of it that it is not the best. Furthermore, Steinbeck has Slim tell George and Lennie:
"You guys better come on while they's still something to eat. Won't be nothing left in a couple of minutes."
Steinbeck was especially gifted for writing dialogue. Good dialogue characterizes the speaker at the same time that it conveys information. Slim's dialogue quoted here characterizes him as a kind and considerate man. He is inviting two strangers to eat even though he knows the food will be rapidly disappearing and he will be competing with George and Lennie for whatever is left. Slim's dialogue also conveys a strong impression of what the scene must be like in the mess hall. We can imagine a gang of hungry men gobbling food as fast as they can and fighting over the remains in the bowls and on the platters. Another picture of life for the workers on a big California ranch!