What does Slim think of Lennie? (End of Part 3)

In OMAM, part 3, George and Slim go into the bunk house together and start up a conversation about Lennie since Slim recently saw him work. Slim now sees how "Maybe [Lennie] ain't bright, but [he] never seen such a worker. He damn near killed his partner buckin' barley. There ain't nobody can keep up with him. God awmighty I never seen such a strong guy" (39). Slim now knows how strong Lennie is but also about how he has an intellectual disability. He begins to wonder why George and Lennie travel together. He thinks that its funny how "a cuckoo like him and a smart little guy like [George] [are] travelin' together" (39). We can see that Slim admires Lennie's strength but thinks that Lennie is a crazy man. George gets a little defensive of this and states that Lennie is not crazy just flat out dumb. Slim just sits back and listens to what George has to say.