There warn't nothing to do now but to look out sharp for the town, and not pass it without seeing it. He said he'd be mighty sure to see it, because he'd be a free man the minute he seen it, but if he missed it he'd be in a slave country again and no more show for freedom. Every little while he jumps up and says:
"Dah she is?"
But it warn't. It was Jack-o'-lanterns, or lightning bugs; so he set down again, and went to watching, same as before. Jim said it made him all over trembly and feverish to be so close to freedom. Well, I can tell you it made me all over trembly and feverish, too, to hear him, because I begun to get it through my head that he was most free—and who was to blame for it? Why, me. I couldn't get that out of my conscience, no how nor no way. It got to troubling me so I couldn't rest; I couldn't stay still in one place. It hadn't ever come home to me before, what this thing was that I was doing. But now it did; and it stayed with me, and scorched me more and more. I tried to make out to myself that I warn't to blame, because I didn't run Jim off from his rightful owner; but it warn't no use, conscience up and says, every time, "But you knowed he was running for his freedom, and you could a paddled ashore and told somebody."
-- Mark Twain, The Adventures of Huckleberry Finn
What themes, genres, or characteristics of the Realist period are represented in the following passage?