Have you ever listened to a Gallic service? In the Scottish Kirk, (in the Highlands and the Isles) the Precentor sings the first notes, and the congregation slowly slides up until they also hit the note. It's so beautiful and strange it makes the hairs on the back of your neck stand up! If someone is a bit 'tone deaf' they can slide up until the note is reached, and if they're a bit 'off' it only adds to the haunting quality of the singing. (You can hear all this on Youtube.)