I’ve found sea urchin shells on the beach before, but never with teeth, probably because they’re pretty delicate.
I knew that they grazed on algae, but I didn’t know that their teeth were so, well, teeth-like.
I also didn’t know what this National Geographic site informed me: “a recent study found that the sound of their teeth scraping on reefs can cause a rise in ocean noise.”
Oh, and why the title? You can read about it here.