The Human Marvels has a great post about the story of "The Two-Headed Nightingale", a conjoined twin named Millie and Christine: how they were sold as slaves, marketed as freaks, and then gained fame for their incredible singing talents:
Throughout much of their life, Millie and Christine were often considered one person. Due to their shared body, it was often unclear if the girls were legally and physically a single being or individuals. The girls themselves often referred to themselves in the singular, using ‘I’ in the place of ‘we’. Joseph Jr. saw opportunity in this confusion and opted to advertise the girls from a new perspective.
The girls became Millie-Christine, a girl with two heads, four arms and four legs.
The concept of such an incredible phenomenon drew immediate crowds and Millie-Christine enjoyed immediate and world-wide popularity. Furthermore, it was the singing of ‘The Two-Headed Nightingale’ that quickly gained predominance over appearance and Millie-Christine eventually performed for European royalty, including the Prince of Wales and Queen Victoria. Mille-Christine became renowned for singing, playing the guitar and piano in unison and dancing the waltz in front of thousands of people in the greatest halls and venues of the world.