Doctor Who: 10 Awesome Moments From Series 6's US Two-Parter

5. The Nano-Recorders

After discovering that the Silence had the ability to erase themselves from their memories, the Doctor devised a plan to help himself and his companions remember what they learned about their enemy. Up to then, the TARDIS crew would draw tally marks on their arms to serve as reminders that they had seen a Silent. The more marks they drew, the more Silence they had seen. But they needed a way to remember more details about the Silence. The Doctor's solution was to inject Amy, Rory, River and FBI agent Canton Everett Delaware III (whose older self was a witness to the Doctor's death at Lake Silencio) with nano-recorders, tiny recording machines inserted underneath the skin that would flash when a message had been recorded. In this way they could save whatever information they learned about the Silence. They would forget as soon as they looked away, of course, but as long as they were looking at the Silence while recording the message, the data would be saved. The nano-recorders added an extra level of creepiness to Day of the Moon. Because they flashed after a message had been recorded, it was always an unsettling reminder that you never remember seeing the Silence, so to have proof of doing something you don't actually remember doing is a bit unsettling.