Welcome to Your Daily Nerd Thing. Our Doctor Who countdown continues this time not with a specific episode but with the creatures. The Silence were hinted at for a long time before they finally appeared in The Impossible Astronaut and then were a feature of a season long story.
The most horrifying thing about the Silence is that you can’t remember them. The moment you stop looking at them you forget they exist. How can you fight something you don’t remember? Of course the Doctor comes up with a solution but not before a lot of very creepy stuff happens with trying to just figure out what they are up against.