9. The Silence In Series 5
http://www.youtube.com/watch?v=P6wczbYfip4 Prisoner Zero told us in 'The Eleventh Hour' that "Silence would fall". The Silence bubbled under the surface of the series, mentioned again in 'Vampires in Venice', but never actually with an explanation of what they were; it was creepy foreshadowing... but what if it went all that much further? There are countless theories on the internet of fans claiming they've seen the Silence in Series 5 there are sightings of cloaked figures and reports of a reflection in 'Amy's Choice', and then there are the numerous instances where the Doctor or Amy look lost or confused. The problem with memory-wiping monsters is that they could've been and gone, and we might not have seen them. The Silence could've had their own subplot within the series visiting Barcelona for the dogs, comparing head shininess with the Ood, stealing Bessie and driving around the country sampling exotic cheeses and cooking raspberry pie and we'd have never noticed. There's no denying that there are instances where we feel like we've skipped a scene. Someone will turn around a bit quickly and wonder where they are, or there'll be something there in the corner of your eye. If that's intentional, it only adds to the genius of the arc. If it's not, it must be scarier to work on Doctor Who than one first imagined.