Q. If one is hearing Kiddush from his rabbi, and the rabbi makes a mistake in Kiddush by saying the yom tov Kiddush instead of Shabbos, and the talmid realizes this during Kiddush, what is the appropriate way to communicate to the rabbi that he is making a mistake and to stop him from continuing with the yom tov Kiddush and saying Hashem’s name in vain? (One cannot talk during Kiddush.) Should one cough loudly or bang on the table?
Once the rabbi is informed of his mistake, from where should he continue? Are the wrong words a hefsek? I assume that he should just go back and say the right words, but without repeating Baruch ata Hashem Elokeinu.

A. Horav Shlomo Miller’s Shlit’a opinion is that the listener should just say aloud the missing correct words, such as; “Asher Kideshonu Bemitzvoisov Verotzo Bonu” in this case, and the person reciting will certainly become aware of his mistake. Saying the correct words is not a hefsek and the reciter does not have to repeat the beginning of the brocho.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a