When a woman (or, if need be, a man) lights candles for Shabbat, she covers her eyes before making the bracha to "pretend" that the candles aren't lit yet because we generally say the bracha before fulfilling the mitzvah, but once the bracha has been made, shabbat would start and she would be unable to light the candles. [Rm"a [quoting the Maharil] in Shulchan Aruch, Orach Chaim 263:5].
Are there any other mitzvot that we fulfill using some measure of pretense? I'm not talking about having a tnai in mind, or doing something incorrectly or incompletely until the bracha is made (like holding an etrog upside down), but about having to pretend that something is different from what it is.