Yaks are made for high altitude. Their lungs and hearts are bigger than other cattle's, which means they can use thin mountain air much better. They are perfectly happy at 4,000 metres - higher than the tallest mountain in Europe.
Yak milk is creamy and rich. People in the mountains use it to make butter, cheese (called chhurpi - which can be so hard you have to chew it for hours), and yoghurt. The butter is also used in tea, melted into a salty drink that warms you up on a cold mountain morning.
Yak wool is spun into rope, blankets and warm clothes. The very softest fur, from the under-layer, makes a fabric a bit like cashmere - light and warm at the same time. Some Nepali villages still weave yak wool the way their great-grandparents did.
Yaks are calm, patient animals. Mountain children grow up running between them and helping look after them. A loaded yak can carry as much as a small horse, walking steadily uphill for hours. They are one reason mountain communities can live in places where roads cannot reach.