Snell's window is the term for the way that light travels downward through water in a cone shape, ending at a point at the submerged viewer's eye. It doesn't hold true in muddy water like Piya finds herself in. When she can't figure out which way is up and feels mud in her nose and mouth, she panics. Something touches her, and she convulses, knowing it's a crocodile snout. She flails, but something strikes her in the face. Suddenly, she breaks the surface but still can't breathe. She notices arms around her, and someone's mouth meets hers to suck the mud out of her mouth. Piya knows that Fokir saved her.
The simple fact that Snell's window doesn't hold true in the Sundarbans—where the water is extremely muddy—suggests that the Sundarbans are a place where commonly held beliefs (even scientific ones) must be cast aside, and new ways of understanding must be discovered. In this case, Piya has to learn to trust Fokir to save her, given that her own scientific knowledge isn't enough to allow her to save herself.
Piya goes still so that Fokir can swim back to his boat. When he tosses her over the edge she starts choking again, and Fokir sucks more mud out of her mouth and throat. Piya notices the forest guard and Mejda on their boat, gesturing for her to hurry up and come back. Piya doesn't want to go with them if she doesn't have to, so she turns to Fokir and says, "Lusibari, Mashima?" He nods and smiles. Piya then turns to the guard and asks for her backpacks. After asking for a hefty fee, the guard hands them over but keeps her Walkman. Piya doesn't care, especially when the guard mimes masturbating at her.
The lack of concern on the part of Mejda and the forest guard tells Piya everything she needs to know—those men don't have her best interests at heart, and it's possible they wouldn't have even cared if she drowned. Using this information, Piya is able to make a decision to work with someone who is far more willing to treat her with respect, despite the communication difficulties between them.