Norah Jones and Queens of the Stone Age frontman Joshua Homme are not an obvious pairing on paper, which is exactly what makes their conversation on Season 2 Episode 18 of “Norah Jones Is Playing Along” so consistently surprising and engaging. The discussion wanders from the inherent creepiness of nursery rhymes to the human nature of music to the story behind Homme’s project Alive in the Catacombs, with a few songs performed along the way that fit the Valentine’s-ready mood Jones sets up around them. Homme is candid and genuinely funny, Jones is the ideal host for this kind of freeform musical conversation, and the chemistry between two artists who exist in completely different corners of the music world but share a deep seriousness about craft makes every tangent worth following.