The correct answer is the second option: The whirlpool is compared to a mouth, showing its menacing threat.
In this excerpt, the narrator is describing his disastrous and terrifying experience of witnessing a whirlpool with some other "men". To describe their fear of being pulled down into the sea by a whirlpool, the whirlpool is described as having a "yawning mouth", ready to "devour" (swallow up) the narrator and the men with him.
