Determining the likeness of a verbatim or parody text to its original is infuriating. Other than estimating the percentage of two things' likeness, I'm not sure how exactly courts judge whether an item falls under Fair Use or not. If likeness basements or ceilings existed (which I don't see how they couldn't), the substantiality in Fair Use cases might be easier to ascertain. That sort of practice is already apparent in Fair Use not covering the "heart" of intellectual property -- so couldn't the "heart" of something be weighted more heavily in a percentage? And I'm still wrestling with how assembled ideas can be unique enough for copyright. This is obviously a question deeper than a four-month class can handle, but -- does a thing have to be unique or significantly unique?