Doctor Who: 13 Cool Details Steven Moffat Just Revealed About The Girl In The Fireplace
10. This Is How The Doctor Could Tell The Clockwork Droids Were Scanning Reinette's Brain
Just after that shot of Paris, the Doctor has his first run-in with a clockwork droid, before discovering that the villains have been "scanning" Reinette's brain.
When you watch the episode normally, it's not really clear how the Doctor knows about the brain scanning thing - he just grabs her head, looks at her for a second, and then makes that assertion.
As Doctor Who fans, we're used to explaining unusual things by saying "well... it's because the Doctor is really clever!" but in this case, we have more of an explanation than that.
According to Moffat, the Doctor knows that Reinette's brain is being scanned because of her irises. Presumably, they look different in some way, and he's able to use this information to deduce what the droids have been doing.