Reindeers can see in ultraviolet light. This is so they can see white against white predators, such as the Polar Bear. They can also see the yellow of a urine trail of a potential predator.
The Reindeer (Ragnifer Tarandus) coat is made up of two layers - a dense inner layer and an outer layer which is made of hollow individual hair shafts, which trap air that their body then heats.
Their sense of sight and hearing aren't brilliant, so they rely mainly on their great sense of smell.
When they walk they make a clicking sound - this is a tendon in their foot passing over the bone. This enables them to communicate with each other in bad weather conditions.
They have an inner, secondary eyelid which they can use to prevent their eyeball from freezing.
They have hair in their nostrils and ears which they can close up to prevent their inner organs from freezing.
Both males and females have antlers which they shed and regrow annually.
