"Smile" actually comes up alot in this episode.
KOR: Good. You will be taught how to use it. Where is your smile?
KIRK: My what?
KOR: The stupid, idiotic smile everyone else seems to be wearing.
KOR: I need your obedience. Nothing more. Will I have it?
KIRK: You seem to be in command.
KOR: Yes. I am. I shall need a representative from among you. Liaison between the forces of the occupation and the civil population. Smile and smile. I don't trust men who smile too much. You, Baroner, you're the man.
KIRK: Me? I don't want the job.
KIRK: Is that's all you can do, smile?
AYELBORNE: You are free, Captain.
KIRK: I want to know how I'm free, and why.