Initially, the boss is suspicious when he learns that Lennie and George travel together. George tells the boss that he and Lennie are cousins and that Lennie was kicked in the head by a horse. The boss is still suspicious, wondering if George is taking Lennie's pay. He warns George not to try to get away with anything like this.

When Slim first asks if George and Lennie travel together, his tone is "friendly" and "inviting." George adds that Lennie is a great worker and Slim appreciates the sentiment. George tells Slim that they look after each other and Slim, unlike the boss, seems to understand and appreciate this: 

"Ain't many guys travel around together," he mused. "I don't know why. Maybe ever'body in the whole damn world is scared of each other."

When Slim is introduced into the novel, Steinbeck immediately draws a very distinct contrast between him and the other characters. In addition to his extraordinary skills as a jerkline skinner (Steinbeck refers to Slim as "the prince of the ranch"), Slim possesses personal qualities that set him apart in a spiritual way: "His ear heard more than was said to him, and his slow speech had overtones not of thought, but of understanding beyond thought." Having established Slim's nature, Steinbeck then introduces him to George and Lennie in Chapter 2.

Slim approves of George and Lennie immediately. Taking a seat across from George, Slim expresses the hope that he and Lennie will join his team on the ranch. When George gives Lennie a compliment, Slim approves, noticing George's smile. It is at this point that Slim asks, "You guys travel around together?" His tone is "friendly," one that "invited confidence without demanding it." George explains, "Sure . . . We kinda look after each other." Slim's reaction reveals his wisdom as he recognizes a profound truth of the human condition:

Ain't many guys travel around together . . . I don't know why. Maybe ever'body in the whole damn world is scared of each other.

The odd couple, George and Lennie, travel everywhere together. As someone with serious learning disabilities, Lennie is incapable of looking after himself. And George promised Lennie's Aunt Clara that he'd always take care of him. So they go everywhere together, from one farm to another, from adventure to adventure.

Slim's an old hand, and he's seen pretty much everything in this business. So he knows just how unusual it is for itinerant farm hands to travel around together. As he points out, the life of a farm hand is a pretty lonely one; he never puts down any roots or establishes any lasting connections with anyone. Instead, he just moves from place to place by himself, works for about a month on a farm, and then quits and takes off his own.