Answer: He tells them about the rock quarry.
Puli is a child affected with leprosy who lives in the streets of the city. When Nathan and Ruku move to the city, they meet him, and he tells them about the rock quarry. This allows the couple to earn some money, especially as they want to go back to their village. Puli becomes very close to them, and they trust him and care for him as if he was their own son.