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The Workbook has two large sections: Strange Things and Normal Things. Everything on the website falls under one of these categories, even if a page is not specifically mentioned as either. For instance, Mount Louigi is not listed under any of these categories, but it is obviously a Normal Thing.
There is no clear definition of what constitutes a Strange or a Normal Thing. Understanding comes with time, and eventually a person is able to correctly categorize any object, phenomenon or event, both within the Workbook and in the outside world.