How did the conversation between Sai Baba and Nana about the Gita verse begin?

The dialogue, which is beautifully narrated in Chapter 39, started when Sai Baba noticed Nana Chandorkar humming or muttering something to himself. Baba paused and asked Nana to speak the verse clearly and slowly so He could hear it. Taking this as a command, Nana recited all four lines of the verse from the Gita. Immediately after, Baba asked Nana to provide a detailed explanation of its meaning. This interaction was intentionally initiated by Baba to impress a true teaching upon Nana, setting the stage for a unique interpretation of the sacred text.