In Christian traditions, "sin" and "death" are depicted as black figures associated with the night, evil, and darkness. Huck isn't religious and doesn't much care for the Bible, but, as we've seen, he's comfortable using its stories and imagery for his own purposes. Here, he equates darkness and sin to enhance the feeling of foreboding created by the storm and to suggest that there's danger ahead.
"it was as bright as glory..."See in text(Chapter IX)
Twain's rough, colloquial language turns lyrical in this passage, as he describes the storm from Huck's point of view. Here, Huck speaks of lightning as a flash of "glory," emphasizing his awe and wonder in the face of nature. Huck has a strong relationship with and affinity for the natural world, as we've seen, and this gives the reader insight into his emotional life. Nature isn't just the only place Huck feels comfortable. It's also the only place he sees real beauty.
"to coat it over so and make a ball of it..."See in text(Chapter X)
When foreign objects like this spool are introduced into the digestive tract, many animals, whales in particular, secrete a substance that will coat the object and protect it from damaging the intestinal lining. This substance is called ambergris in whales and coats the sharp points of squid beaks to allow them to pass. Here, the catfish is described as having "lots of rubbage" in its stomach, which testifies to the pollution of the Mississippi River.
"spread himself out so that he was just a kind of a layer..."See in text(Chapter X)
Twain lessens the impact of this gruesome description for the reader by making it impossible and almost cartoonish in its violence. Indeed, much of the violence in the novel seems cartoonish, divorced as it is from a basic understanding of anatomy, medicine, and even the laws of physics. Jim's snakebite, for example, couldn't possibly have been cured by drinking whiskey, because its alcohol content wouldn't have cleansed the wound unless it was poured directly over it; and yet, we believe that it happens because it's told with such confidence.
"it had took all that time to come over the water..."See in text(Chapter XIX)
Recall that in Chapter VII Twain used the sounds of a ferry landing to indicate that it was both far away and that Huck was moving away at a rapid speed. Here, he builds on that same concept of distance and sound to indicate the grandeur of nature and the astonishing width of the Mississippi, which he describes as being a mile and a half wide.
