DURING my master’s degree, I lived high up in the mountains of rural Ecuador, studying the practices of traditional Andean medicine. I was fascinated by beliefs of culturally specific syndromes , like susto , thought to be caused by spiritual attack, resulting in insomnia, depression and anorexia, or mal de ojo , in which a stare from another person can cause severe fever, diarrhoea and even death in children.

What always stood out when I asked about the basis of …