To clarify and deepen my understanding of the Book, I pondered the following comparisons with similar and/or opposing cards. Maybe my comparisons will inspire you to make your own!
Knowledge
Book: Factual knowledge; educated. "I know this!"
Bear: Practical knowledge - capable. "I know how to do this!"
Snake: Thirsty for knowledge. "I want to know!"
Secrets
Book: A "secret" in the sense of esoteric knowledge - not everyone has access to some type of knowledge or information.
Clouds: Something is being hidden from view, fogged over - not necessarily with bad intentions, possibly just for self-protections or out of shame.
Mice: Harmful and/or malicious secrecy. Something is being done behind someone's back. Sneakiness.
Key: The opposite of secretiveness: openness, straightforwardness. Or: to find access to a secret.
Birds: To blab a secret.
Intelligence
Book: Intelligent in the sense of well-educated, knowledgeable.
Snake: Diplomatic intelligence, great rhetoric; acumen; ability to direct (even manipulate) others.
Fox: To be street-wise. Cunning; and the intelligence of knowing when to risk something and when not to.
Facts vs. information
Book: Facts; the truth.
Letter: Information. Some content is being shared, passed on, expressed - while this content could be factual it doesn't have to be; the information shared could be false, too.
Categorisation
Book:
To categorise something; something can be categorised, intellectually understood.
Wild Card:
Something doesn't fit into the usual categories. Something is impossible to understand intellectually because we can't categorise it (yet).
