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Hippos are the surprising stars of the last part of this fascinating series. It turns out they’re the unsung heroes of Africa – the entire river ecosystem depends on hippos. Once night falls, they emerge from the water to graze on grass for seven hours.

What goes in, must come out, so brace yourself for the footage. But it’s all for a purpose – the hippos’ unique anatomy helps them spread their nutrient-rich dung widely, stimulating the entire food chain in Africa’s rivers.