In an article, published in The Boston Globe last week, historian Marcus Rediker, who teaches at the University of Pittsburgh, reminds us that, in 1807, Great Britain and the United States ended the African slave trade. On that important anniversary, he has published a new volume, The Slave Ship: A Human History. As he researched, in England, Rediker came across a strange, sickening satire, called "The Petition of the Sharks of Africa." In it, sharks plea with parliamentarians not to end the slave trade, lest the carnivorous fishes starve. Rediker writes, "Nothing I had ever read had prepared me for such a document. Here, unexpectedly, was a dark and daring kind of humor that I had never known to exist among abolitionists." The author will be with us, in the second hour, to talk about the broadside he discovered in Bristol, and the slave trade. Does this document surprise you? When is satire inappropriate?