In one section of the famous Codex Mendoza displayed in the Museum of Anthropology in Mexico City shows a man offering human arms to a maiden to woo her. The practice of cutting off arms of soldiers in battle, which we associate with the missionary Ammon cutting off the arms of robbers was an ancient Mayan war tradition which was a sign of status to a warrior.
The swords that were used in Book of Mormon times were made of obsidian. They had a blunt side and a very sharp side and could be used to kill, to knock out, and to injure. To cut off the arms, Ammon used the edge of the sword. Brother Yerman sited other mentionings of swords in the Book of Mormon. In Alma 43:44, there is more smiting of arms. In Alma 26:3, Ammon rejoices in his ability to serve as an instrument of God. He knew what tactics and strategies to use in dealing with Limhi and his people.