How does Huck's practical joke on Jim humanize Huck? What was Twain's purpose in this passage?

Huck tries to play a trick on Jim by telling him that the events of the night before were just a dream. After some convincing, Jim starts to interpret the "dream." After some time, Huck finally points out the leaves and debris left from the night before, at which point Jim gets mad at Huck for playing such a mean trick on him. Huck feels terrible about what he did and apologizes to Jim. The joke is malicious or based on race, it is a simple joke. I think this makes their relationship more human. It shows that Huck understands Jim and the way he thinks.