Sarah Thornton had never thought much about her breasts. But after undergoing a double mastectomy, the sociologist found herself thinking deeply about what she'd lost as a woman – and the complicated relationship our society has with breasts. Thornton's experience inspired her to speak with scores of people, from plastic surgeons, to bra designers and milk bankers. She joins Piya Chattopadhyay to share what she learned from them about the power and politics of breasts, as explored in her book Tits Up.