Capt. Malcolm Reynolds: I know she meant to kill me 'fore the Doc put her to sleep, which how exactly does that work anyhow?
Dr. Simon Tam: Safeword. The people who helped me break River out - they had intel that River and the other subjects were being embedded with behavioral conditioning. They taught me a safeword, in case... something happened.
Kaylee Frye: Not sure I get it.
Dr. Simon Tam: A phrase that's encoded in her brain, that makes her fall asleep. If I speak the words, "Eta...
Jayne Cobb: Well don't say it!
Zoë: It only works on her, Jayne.
Jayne Cobb: Oh... Well, now I know that.