Plot hole: When Neptune places the curse on Emily, her hands begin to become webbed but never once does she have webbed hands when she is a mermaid so the curse shouldn't cause this. She isn't becoming something that she isn't, she is becoming half mer half human, so the curse shouldn't affect her hands because they never actually transform when she changes into a mermaid, only her lower half changes. Even the pictures in the book show hands that aren't webbed when in mermaid form.