The indigenous people of the Amazon rainforest practice a sustainable method of shifting cultivation. They clear small areas of land by cutting down trees and burning them to create space for growing crops. After several harvests, as the soil nutrients are depleted, they move to new areas to farm and allow the previous areas to recover for around 50 years. However, increased commercial development in the Amazon has reduced available land, forcing the indigenous people to return to areas before they have fully recovered. They are also threatened by diseases they have no immunity against. The document also warns about the candiru fish, which can swim into and latch inside the human urethra, requiring surgical removal.