From Two Live Crew's controversial comedy to Ice Cube's gangsta styling and the battle rhymes of a streetcorner cypher, rap has always drawn on deep traditions of African American poetic word-play, In Talking About Your Mama, author Elijah Wald explores one of the most potent sources of rap: the viciously funny, outrageously inventive insult game known as "the dozens."

So what is the dozens? At its simplest, it's a comic chain of "yo' mama" jokes. At its most complex, it's an intricate form o...