"Neither had I, until I saw it for myself." She shrugs. "I guess 'Shadow' was just the most accurate word for a property that really doesn't have a word at all. See, it's more that the frequencies cancel specifically in the focus planes at a theoretical right rotational angle to the... uh... y-you know how you shine light through different colored lenses, and all together they produce white again? I believe it's something like that. Only it's not white. It's dark." She tries to simplify.