Coming from Doctor Who, where the order known as the Silence are "memory-proof", so you can only remember them while you look at them, and you forget them when you look away. The Silence uses post-hypnotic suggestion to make people do their bidding without people realizing what they're doing or why.
Amy: "What is it?"
Doctor: "Uhh… I forget…."
Rory: "Hah. You just Silented!"