Well, I think, I certainly used backward music in Sea of Monsters. I can't remember in the Sea of Time. I would tend to do that all the time, you know? I tended to do all sorts of weird things. Just to get effects. ↗
When I was first learning songs, I'd have a favorite song, and I'd take the chords and twist them around. I'd learn the chords and then play them backward. That was my first experimenting with writing a song. ↗