Words to Your Mother: Baleen
Long story short, baleen is whale teeth.
(Waits for any cetacean biologists reading this to finish cringing.)
Technically speaking, whales don't have teeth or any real equivalents. Baleen provides a filtering system for whales (or, more specifically, baleen whales) to strain items such as krill out of the water, basically allowing them to float around without spending too much effort eating.
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