The males' enormous nose is not a mistake - it is what makes them attractive. The bigger and droopier the nose, the more impressive a male is to other monkeys. The nose also acts like a microphone, making their honking calls louder and deeper across the forest. Females have smaller, neater noses.
Proboscis monkeys are amazing swimmers. They live in the mangrove forests where Borneo's rivers meet the sea, and they often jump straight out of the trees into the water with a giant splash. They have partly-webbed fingers and toes that help them paddle. They can even swim underwater for short distances.
Their orange-pink colouring makes them look a bit like they have an permanent suntan. Their round bellies are not because they over-eat - they are full of helpful bacteria that break down leaves. Proboscis monkeys eat mainly leaves and unripe fruit, which is hard to digest. Their special stomach is a built-in factory.
Visitors to Borneo's rivers often see whole families of proboscis monkeys lined up on branches at sunset, like an audience at the cinema. The babies have blue-grey faces and tiny noses that slowly grow bigger as they get older. Conservation groups in Malaysia work hard to protect their mangrove homes.