What is narwhal 'horn' really made of?
It is a canine tooth. Usually, males have a single long tusk, the canine on the left side of the upper jaw that projects through the lip and forms a left-handed helix. The tusk grows throughout life, reaching length of 3 m (10 ft). In some rare cases, both canines grow equally long, forming two tusks. In the Middle Ages, narwhal tusks were sold as unicorn horns.