Twain uses the language of the traditional southern duel in describing the banter between Roxy and Jasper.  This imagery pattern exemplifies Twain's use of the south's own traditions as a means of taking them apart.  From Encarta.com:

                         du·el [dl ] noun (plural du·els)

                         1.  formal fight over matter of honor:  a
                         prearranged combat, especially in former
                         times, between two people with lethal
                         weapons, usually to settle a disagreement
                         over a matter of honor.  The combatants
                         were usually accompanied by seconds or
                         supporters.
                         2.  struggle between two parties:  a struggle
                         or conflict between two people or groups
                         intransitive verb (past du·eled, past
                         participle du·eled, present participle
                         du·el·ing, 3rd person present singular
                         du·els)

                         1.  engage in one-on-one combat:  to fight
                         somebody one-on-one, typically with
                         firearms or sabers and usually over a matter
                         of honor
                         2.  oppose:  to be involved in a conflict or
                         struggle with somebody

                         [15th century. From medieval Latin duellum
                         "combat between two persons," from (by
                         folk etymology from Latin duo "two")
                         Latin duellum , an archaic form of bellum
                         "war."]