Not classified info at all, just not explicitly stated because I'm not sure if Oda is going to piss all over my theory. If you haven't read beyond Thriller Bark, feel free not to read this though. When they're fighting the Flying Fish Gang, Brook sends the enemy to sleep with his music. So this was inspired by the theory that he can manipulate people, or at least the mood, through that ability. So those five minutes that he requested Zoro give him were spent 'sedating' Sanji, creating a mood where they can physically express all the emotion from the fight with Kuma that they can't say out loud. Hope that makes sense.