For thousands of years, people around the world have modified their bodies with tattoos and piercings. But some cultures, like the ancient Inca in Peru, took that practice beyond skin deep. They sometimes used ropes and boards to slowly change the shape of human skulls. It’s a process called "cranial modification." In this podcast, bioarcheologist Valerie Andrushko explains. Podcast produced by David Levin. Original interview by Melissa Salpietra. NOVA is produced by WGBH in Boston. Funding for NOVA is provided by ExxonMobil, David H. Koch, the Howard Hughes Medical Institute, the Corporation for Public Broadcasting, and public television viewers. To learn more, go to pbs.org/nova/machupicchu