Tom,
We all know full well that errors pop up from time to time and that much effort is put into avoiding them in the first place. Finding them and making them known is what a lot of fans do as they scrutinize every detail and second of every show. Evidence the at least one video on You Tube of errors in some of the episodes of Dr. Who over the years. The video I am referring to is of out takes from missed lines and prop malfunctions. I find them hilarious. They in no way diminish the final product but serve, to me at least, as reminders that the people involved with the show are just normal people, except for Your Good Self of course! I do wonder where those out takes come from...
The question: Can you recall any errors that you noticed as they were happening, or before they happened, that you were able to avoid ending up in the final cut? I'm thinking a something like "The doctor would never say, or do, that!"