This week’s episode of Doctor Who ended on a shocking cliffhanger, with hero the Doctor (Peter Capaldi) revealing that he’d been struck blind after going into space without a helmet and that there was no way to heal his eyes. 

The surprising twist was revealed in one line delivered by the Scottish actor – “I can’t look at anything, ever again – I’m still blind.” – but what viewers might not know is that a lot of thought was put into the expression of this statement, with the programme-makers changing the intonation of the words Capaldi spoke at the very last minute. 

In the preview version of the episode delivered to reviewers, Capaldi’s words were delivered in a sort of monotonous low shout, whereas the finished episode saw them re-dubbed to be more softly spoken and whispered for greater dramatic effect. And in a sign for how last-minute the change was, an official behind-the-scenes video for the episode actually still has the earlier version of the line, which you can see from 1.53 below.

Meanwhile, the finished version (available on BBC iPlayer) can be heard from about 00.22 in the below clip – spot the difference?

Now, such changes aren’t unusual or controversial in any way – the BBC have confirmed to RadioTimes.com that reviewers are usually sent episodes that are works in progress, and that these sort of minor tweaks are common at the final stages – but it is an interesting insight for TV viewers into the sort of last-minute alterations that go into tightening up their favourite shows, as well as a rare example where both versions of the change are available to watch.

And it also gives audiences an insight into the fascinating world of ADR, aka additional dialogue recording, which can be used to quickly alter a TV show late into post-production and is a topic that Doctor Who producer Nikki Wilson discussed at a recent event for earlier series 10 episode Knock Knock.

“Most of the dialogue that you hear is the stuff we’ve recorded on location,” she said, “[But] occasionally, when we get into the edit we find an area where the story’s not quite as clear as we’d have liked, or maybe the sound that was recorded on location was not technically crisp enough.

“And then we’d do what we call ADR, which is additional dialogue recording, which is when we get the cast back to either record a new line or to rerecord the lines they did on set if there’s noisy footsteps in the background or whatever.”

In this case, it seems the production team decided that Capaldi’s earlier version of the dialogue wasn’t quite dramatic enough, resulting in a different audio take recorded by the actor being spliced into the scene to bring the perfect effect. Who else but the Doctor could go back in time to change his own words, eh?

Doctor Who continues on BBC1 this Saturday at 7.25pm