And Then There Were Fewer - S9-E1
Continuity mistake: While everyone is in the secret room Peter finds a blue book on the desk and picks it up to read. Peter's holding this book in his hands when he asks Consuela what happened, and just as Consuela tells him about her nephew, we see another blue book on the desk beside Peter. There should be only one blue book - the one in Peter's hands. (00:20:40)