I think it's "a slim tome"— a book lazily implemented as a container so you can "open" it.
(And yes, your idea there would have been a much better way of implementing a puzzle around this concept!)
Oof, no amount of phoneme shifting can move the stress to the second syllable, I see it. But I'm thrilled that in the lazy implementation, container-ness came through and book-ness did not.
