Abigail: You are out of your mind! This will never work.
The Doctor: Oh! Don’t think shark, think dolphin.
Abigail: A shark isn’t a dolphin!
The Doctor: It’s nearly a dolphin.
Abigail: No, it isn’t.
The Doctor: Well, that’s where you’re wrong, because… Shut up.
Kazran: It could be anywhere. Will it really come?
The Doctor: No chance. Completely Impossible… Except on Christmas.
From the 2010 Doctor Who Christmas Special.