Shelby Van Pelt’s novel Remarkably Bright Creatures spent an extended period on bestseller lists largely through word of mouth — the kind of book readers press on other readers with an insistence that can be off-putting until you actually read it. The premise involves a widow working at an aquarium who forms an unlikely bond with an octopus named Marcellus. It is also a missing-persons mystery and a story about grief and the ways humans project emotional intelligence onto creatures who may or may not share it.