Which is the Most Significant Clue in Recent Episodes of Doctor Who?

The following two quotes are obvious candidates. Which would you pick from the two – or would you propose a different one altogether?

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Doctor Who: Oxygen
Doctor Who: Thin Ice
Doctor Who: Smile
Doctor Who: Knock Knock
  • http://GarySaid.com/ garylapointe

    I choose, “The Doctor lies.  And so do I.”, said by River Song.

  • http://GarySaid.com/ garylapointe

    I choose, “The Doctor lies.  And so do I.”, said by River Song.