What the hell was the Mavity thing about? How could they have known Newton misheard them like that?
Loved the episode. Not what I expected as an anniversary episode, but regardless, this was a really cool monster, and it was great to see this side of the Doctor, which I suppose is what makes it work for the anniversary.
Edit: Also, I hope the edge of the universe comes up again. I'd have liked to see more about that.
What the hell was the Mavity thing about? How could they have known Newton misheard them like that?
They altered time so Newton discovered "Mavity" instead of "Gravity". How The Doctor still knew it as gravity is interesting, but any human would only know it as mavity.
I suspect the mavity bit is either a tease for an upcoming plot point about changing history or just a running gag that will get called back later.
They didn't know Newton misheard them. Couldn't have. Donna said it as 'mavity', and the Doctor gave her a momentary odd look. But then when he said it as 'gravity', she didn't know what he meant and he corrected himself to 'mavity.'
What that means is that history was changed, and the word is now 'mavity' and always has been. Nevermind Latin etymology and the fact that of course Newton didn't actually invent the word but only popularized this specific use for it.
The point was that the change affected Donna but not the Doctor, because he's a Time Lord. Whether it's just a joke or a hint at something to come remains to be seen.