Kanai returns to the notebook. Nirmal asks why the island they're going to is called Garjontola—he wants to know if it comes from the Bengali word for "roar," garjon. Kusum explains that long ago, Kusum's father was caught in a storm. He tied himself to a tree with his gamchha on Garjontola. After the storm passed, he did hear a tiger's roar, but he dreamed of Bon Bibi telling him she'd keep him safe if he was good at heart. Kusum's father later returned to build the shrine. Nirmal is incredulous at the fantastical nature of the story, so he keeps an eye out for opportunities to poke holes in Kusum's fantasy.
Nirmal's question implies that in his eyes, pure and unadulterated language is unparalleled; his dismissiveness of Kusum's story suggests he believes that naming things because of experience is a less valid way of doing things than naming things based on language alone. Again here, the gamchha is a way for Kusum's father to connect with life and in this case, with his religion as well.
Suddenly, Nirmal hears the sound like someone blowing their nose. Fokir points to dolphin backs in the water, and Kusum smiles and says she calls them "Bon Bibi's messengers." One looks right at Nirmal, and he feels as though Rilke himself is looking right at him, saying that animals see right through humans.
When Nirmal sees Rilke in the dolphin, it shows how he's using texts important to him to add more meaning to things he's confronted with in his real life. In doing so, he's better able to understand himself and the people he's with.