Have you ever wondered if slugs can smile — or if they even have teeth? How a slug eats is surprisingly complex!
In geometry, there are surfaces that do without an inside or outside—and some need at least four dimensions to exist ...
It is enamel. Like hair and nails, this hard substance is made by epithelial cells. Once it was thought to be as inert as rock; now it is known to exchange its substance with the body fluids ...
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