To a Klingon, a smile signals not only contentment, satisfaction, and good humor, but also complacency, the feeling that all is well. Klingons are generally apprehensive about those showing too much friendship.

(st.klingon 8/06/1996):  The Klingon word for smile is mon. This also means things like snarl and smirk. I wouldn't be surprised to find a Klingon mon and growl at the same time, but mon by itself doesn't describe the full growling experience.

Do not confuse with the noun mon "capital" [i.e. city].

PUN:

"Mona Lisa" (mon'a' Is she smiling?) Confirmed by MO at qep'a' wejDIch.