The greatest bit of irony in that book is when Huck is talking to a "good Christian woman" about him being on a steam ship whose boiler exploded. When asked if anyone was hurt, he replies, "No'm, killed a nigger." Relieved, she says "That's good."
It was a terrific anti-slavery/anti-racism piece, and yet, year after year, (black or guilt-feeling pansy white) people want it banned from here and there. Maybe someday they'll grow a damned brain.
Off topic, but my favorite Twainism is, "He had the cool confidence of a Christian holding four aces."