Smile and keep silence. Used when you know the answer, but do not want to say it or there is some force stop you from telling it out.
Lucy asked me how do you think of her dance. I think that's bad but I don't want to hurt her, so I just smilence.
Smile meaningfully but keep silence.
Smilence occurs when you know what is going on, but decided not to speak it out. However your smile betrayed your attempt.
You do smilence because that you do not want to hurt others' feeling or harm yourself; or the answer is forbidden to say or too trivial or simply useless.
When the party says that freedom of speech is a fundamental right of Chinese citizen endorsed by the constitution, the shitizens all keep their smilence.
"Why are you smilent! Who do you think is more beautiful, Helen or me?" my girfired asked me.