Slim understands the friendship between George and Lennie. Although he notes that "ain't many guys travel around together", upon refection he concludes, "I don't know why...maybe ever'body in the whole damn world is scared of each other". Slim accepts George and Lennie's friendship as a positive thing, an asset with benefits on which others are missing out (Chapter 2).
Slim is a thoughtful person, with "a gravity in his manner and a quiet so profound that all talk stopped when he spoke...his ear heard more than was said to him, and his slow speech had overtones not of thought, but of understanding beyond thought". While others looked upon George and Lennie's friendship with cynicism, immediately concluding that George must be using Lennie's labor for his own benefit, Slim perceives that their friendship is based on concern and caring (Chapter2).
When George, at the end of the story, feels he must kill Lennie to spare him from an ultimate punishment he could never understand, it is Slim who comprehends how difficult it is for George to carry out his self-appointed task. Slim comforts George, assuring him, "you hadda, George...I swear you hadda", and compassionately taking him off to get a drink, while the others stand by and wonder, "now what the hell ya suppose is eatin' them two guys?" (Chapter 6).
I see how it links in, good point my friend.