Amy: What is that thing?
Captain Avery: A legend. The Siren. Many a merchant ship laden with treasure has fallen prey to her. She’s been hunting us ever since we were becalmed, picking off the injured.
Boatswain: Like a shark. A shark can smell blood.
The Doctor: Okay. Just like a shark. In a dress. And singing. And green! A green singing shark in an evening gown