While this film is a silent with synchronized score, there are two short scenes where Novarro sings a portion of the theme, "Pagan Love Song". First, when he is thrown off the boat by Donald Crisp and toward the climatic end when he lays down, humming the tune, and finds Crisp's cane.
You can hear him tapping the cane against the bamboo hut "live", not added sound. Both of these scenes are in perfect sync (probably Vitaphone--sounds like disc surface noise). You can usually tell the "sound stage sound" as opposed to studio sound added later.
The reason for these two short sequences is probably because the film was filmed "on location" in the Pacific. At that time, location sound recording would have not been practical. The scenes were most likely shot on a sound stage at M-G-M. Many silents were still in production in 1929. Adding sound sequences, or "goat glands", as they were called, was a transitional way of making silents "part-talkies", as referred by Photoplay magazine.
