Off the shore of Brazil, almost due south of the heart of São Paulo, is a Ilha de Queimada Grande (Snake Island). Researchers estimate that on the island live between one and five snakes per square meter. The snakes are a unique species of pit viper, the golden lancehead. Responsible for 90% of Brazilian snakebite-related fatalities. The golden lanceheads that occupy Snake Island grow to well over half a meter long, and they possess a powerful fast-acting poison that melts the flesh around their bites. This place is so dangerous that a permit is required to visit.