Can I get a little help applying some context in a book I’m reading?

I’m reading The Orchard by Yochi Brandes, which is the story of rabbi Akiva Ben Joseph, and it references two things I’m having trouble understanding: “the laws of cucumbers” and “the work of the chariot”. I did some googling and can’t find anything about the laws of cucumbers that makes sense, and I can see that the work of the chariot is related to Jewish mysticism.

My question is: could anyone put these into a bit of context as to why a student wouldn’t be allowed to learn them and what the dangers are? The Wikipedia article on the work of the chariot didn’t provide a ton of clarity to me. I mean, I know that Kabbalah and Jewish mysticism are esoteric and very difficult to study of course (and I want to be clear: I personally have no interest in studying them; I’m specifically just trying to add some context/understand the stakes in this book) but this book implies that there is some kind of danger in learning about it. And then of course if there’s any clarity on what the laws of cucumbers is/are that would be helpful.