I wonder if the Zygons have any way of detecting their own kind even when the Zygon in question is disguised. Presumably not, as they didn't realise that Kate was a human being in this episode, but I have to wonder. After all, they seemed utterly convinced that Osgood was a Zygon. Why else would they make her give that "the enemies of our race will be destroyed wherever they are in the world" speech in the previous episode? Clearly they believed that this Osgood was one of their own...

And I want to take a moment to celebrate the fact that Clara is officially the longest-serving companion of New Who, as expected after she ended up staying on at the end of Last Christmas. Amy previously held this title (having appeared in 33 episodes). But Clara will have appeared in at least 34 episodes by the end of this series (35 if she appears in Hell Bent, which looks highly likely). Obviously I'm not counting Heaven Sent or Asylum of the Daleks, but I am counting The Snowmen since the original Clara Oswald appeared at the end of that episode.

I think that this is one of the best episodes of Doctor Who for years and years. Capaldi knocked it into orbit.

Agreed one of the best episodes, liked the five rounds rapid reference too - episode entry here - http://www.doctorwhoworld.net/ns9ep8

This is the only episode I have enjoyed so far this series. Lets hope it marks a return to form.
Of course the Osgood boxes mean nothing because the real switch is inside our head.The doctor is pressing it to change their minds and alter consciousness.
His speech is the pressing of the button.
And that is Moffat at his best!

excellent episode and two parter, loved the doctors speech at the end, Peter Capaldi was bloody brilliant

Can't help thinking how horribly timely Peter's wonderful speech has turned out to be.

I was actually thinking that last week but its even more so now!