Reindeer are perfectly built for cold. Their fur has two layers - long guard hairs on top and a thick woolly layer underneath that traps warm air. Their hooves are wide and flat, like snowshoes, so they don't sink into snow. In winter, the hoof shrinks and hardens to dig through ice for food.
What do reindeer eat in winter, when everything is covered in snow? Mostly lichen - a small, crusty plant that grows on rocks and the ground. Their amazing noses can smell lichen through 60 cm of snow. They dig down with their hooves to reach it. The Sami call the snow-pit a reindeer makes 'craters'.
The Sami people are the indigenous people of the very north of Norway, Sweden, Finland and Russia. For thousands of years, families have moved with their reindeer herds - from coastal pastures in summer to inland forests in winter. Today, many Sami still herd reindeer. They use snowmobiles, drones and helicopters alongside very old skills.
In our imaginations, reindeer pull Santa's sleigh on Christmas Eve. In real life, Norwegian reindeer don't fly - but Sami families have driven reindeer-pulled sledges across the snow for hundreds of years.