Editor's note: Many performances of Handel's most famous oratorio invite audience participation. These are called Sing-Along Messiahs, Scratch Messiahs, People's Messiahs, and Do-It-Yourself-Messiahs. For this article about performances in which unrehearsed attendees serve as the chorus, we'll refer to each of them as "Messiah."
George Frideric Handel's oratorio "Messiah" shows up in concerts regularly this time of year. But some performances call for the audience to join in.