How does Twain create humor in the tense situation of Pa's drunken rage in the cabin?

Huck knew Pa was going to get drunk, and that he's have his opportunity to steal the key, but he had no idea his Pa would get so drunk that he'd be delusional. He must have been quite a sight dodging snakes, talking about the dead tramp, and calling Huck the angel of death.

"I don't know how long I was asleep, but all of a sudden there was an awful scream and I was up. There was pap looking wild, and skipping around every which way and yelling about snakes. He said they was crawling up his legs; and then he would give a jump and scream, and say one had bit him on the cheek -- but I couldn't see no snakes. He started and run round and round the cabin, hollering "Take him off! take him off! he's biting me on the neck!" I never see a man look so wild in the eyes. Pretty soon he was all fagged out, and fell down panting; then he rolled over and over wonderful fast, kicking things every which way, and striking and grabbing at the air with his hands, and screaming and saying there was devils a-hold of him. He wore out by and by, and laid still a while, moaning. Then he laid stiller, and didn't make a sound. I could hear the owls and the wolves away off in the woods, and it seemed terrible still. He was laying over by the corner. By and by he raised up part way and listened, with his head to one side. He says, very low: "Tramp -- tramp -- tramp; that's the dead; tramp -- tramp -- tramp; they're coming after me; but I won't go. Oh, they're here! don't touch me -- don't! hands off -- they're cold; let go. Oh, let a poor devil alone!"

Then he went down on all fours and crawled off, begging them to let him alone, and he rolled himself up in his blanket and wallowed in under the old pine table, still a-begging; and then he went to crying. I could hear him through the blanket.

By and by he rolled out and jumped up on his feet looking wild, and he see me and went for me. He chased me round and round the place with a clasp-knife, calling me the Angel of Death, and saying he would kill me, and then I couldn't come for him no more. I begged, and told him I was only Huck; but he laughed such a screechy laugh, and roared and cussed, and kept on chasing me up. Once when I turned short and dodged under his arm he made a grab and got me by the jacket between my shoulders, and I thought I was gone; but I slid out of the jacket quick as lightning, and saved myself. Pretty soon he was all tired out, and dropped down with his back against the door, and said he would rest a minute and then kill me. He put his knife under him, and said he would sleep and get strong, and then he would see who was who."