A person is listening to his friend make Kiddush on Fri night with intent to be yotzi. The friend does not enunciate the words properly, swallows words, says it too quietly, and the listener realizes that he cannot be yotzi with this blessing because he is unable to hear the words. Should he answer Amein at the conclusion of the blessing?
He can say Amen at the conclusion of the blessing.
O:CH 215:2 & Mishnah Berurah 6, Biur Halacha ד”ה שלא