Doctor Who: 13 Cool Details Revealed In Steven Moffat's Time Of Angels Commentary
7. The Beach Scene Switches Filming Locations Halfway Through
When the Doctor and Amy first exit the TARDIS and have a chat with River, this scene - set on a beach on the planet Alfava Metraxis - was shot on an actual beach in Wales.
Then, when Father Octavian arrives later in this same scene, the characters are still supposed to be on that Metraxis beach. But in reality, the crew has now moved to a completely different location: one of Doctor Who's signature quarries.
This is why the conversation with Octavian - on the "beach" - has such a blurry background: the crew were trying to mask the shift in location.
The quarry was then used for the very next scene, where Octavian and his clerics have set up a base camp at night. But again, in the world of the episode, this is still supposed to be the Metraxis beach.