As the character is heading towards the mermaid, he stumbles upon a root and falls down. When he looks up again, the mermaid's face is red with anger because of the interruption. This gives him enough time to realise that if he doesn't run away right now, he's going to be swallowed by her, and she looks quite hungry. Turning around, and covering his ears, he just runs into the forest's depths trying to get away far enough from the lake not to hear that voice again, or see that angry gluttonous face.