Spring Heel Jack (not to be confused with the ska band Spring Heeled Jack) were innovators of what I’d call avant-junglism. Early on (Busy, Curious, Thirsty was originally issued in 1996) the duo realized that jungle’s conventions allowed plenty of room for experimentation, and they went there with a vengeance. Check out the way jazz horns and awkward side effects get together and dance on “Bells,” for example, or the frantically fragmented orchestral samples on “Happy Baby.” This is jungle as art music, not as dance music.