There is a huge thunderstorm while the raft is going down the river.  The thunder and lightning add excitement to the story.  The storm makes the reader believe something exciting is going to happen.

Huck does not want to cause any trouble.  He knows he is a runaway and does not want himself or Jim to be caught.  The con men are more likely to think about themselves if they knew there was a reward involved.

Jim believes the moon created the stars.  He has seen frogs lay eggs and compares the moon to the frog.