sentence: All narwhals have two teeth in their upper jaw.
sentences_after: After the first year of a male narwhal's life, its left tooth grows outward, spirally. Tusks are usually twisted in a counterclockwise direction and are hollow inside. The tusk is not used in hunting. In fact, when people found the horn of a dead narwhal washed up on shore, they thought that they had found the horn of a unicorn. Daston, Lorraine and Katharine Park.
concept_name: narwhal
headings: Narwhal Description
categories: Toothed whales