A grown water buffalo can weigh nearly a tonne - about the same as a small car. Despite their size, they are famously calm and patient animals. Vietnamese children who grow up in the countryside often help look after them, leading them between fields by a soft rope.
Water buffaloes are made for muddy ground. Their hooves are wide and splayed, like four little snowshoes, so they can walk easily across soft rice paddies without sinking. They are also wonderful swimmers - if a river is in the way, a buffalo will simply walk in and paddle across.
They love water for another reason too. On a hot Vietnamese afternoon, a buffalo will wade into a pond or river until only its head sticks out. The cool mud sticks to its skin and helps keep biting flies off. You'll sometimes see white birds called egrets standing on a buffalo's back, eating insects - the buffalo doesn't mind, and the bird gets lunch.
On many old village banknotes and stamps in Vietnam, you'll find a picture of a buffalo with a child sitting on its back, watching the sun set over a rice field. It is a much-loved image - quiet, hardworking, and patient.