7. The Only River In The Forest
http://www.youtube.com/watch?v=Yp4GlahYjeg When Idris was dying in 'The Doctor's Wife', Rory claimed that she kept repeating the same phrase over and over again: "The only water in the Forest is the River." We all sort of knew what that was referring to, and later on, it was to be confirmed in 'A Good Man Goes to War' that the people of the Gamma Forests don't have a word for Pond. There are no ponds in the forest, and "the only water in the Forest is the River." But this is actually a clue that relates back to a previous episode. It has to be, really it's River, and her timeline's out of sync with ours. River Song ends up in The Library. Of course, there are connotations of silence too, but the title of River's last chronological episode, 'Forest of the Dead', also furthers connects with the Gamma prophecy. There's unlikely to be any water in a forest so dead, and whilst this is not so much a clue, but a connotation, it certainly has significance for anyone wanting to watch the River episodes in their correct order.