Narwhals have nature's only straight tusk, a single tooth up to three meters (10 feet) long, so strange they were sold as magical unicorn horns during the Middle Ages.
The tusk/tooth is made of two different materials one inside and one outside. They spiral in different directions and that apparently keeps it straight
The tusk/tooth is made of two different materials one inside and one outside. They spiral in different directions and that apparently keeps it straight