The Doctor was very sure about Clara not being killed by the toxin so it could mean that he knows that she isn’t human because he survived the toxin because he was Time Lord.

Maybe if Clara is shown other pictures of her other self’s, like the Victorian London one then maybe she may remember what the Doctor said to her in the Journey to the center of the TARDIS about her other selfs […]

Just re-watched utopia and before the master became Time Lord again he was a professor. There was a professor in this episode and last episode, the on in Cold War also seemed quite strange, which could be hinting […]