The Planet of the Apes prequels did much to explain how humans lost their status as the dominant species on the planet -- a cataclysmic set of events fuelled by a global pandemic known as the "Simian Flu". This virus, the product of a medical experiment gone horribly wrong, wiped out the vast majority of humans, but it boosted the brains of apes. And in the latest instalment of the franchise, the virus has mutated into an insidious new form, affecting humans in some disturbing new ways.