Foster said the song's key was "too high for him"; the voices did not harmonize well.

And their three voices harmonized exquisitely.

They sang it in their- sweet true children's voices, the girls harmonizing and clapping in spontaneous rhythm.

When the four voices harmonize, they find a rough, very tenuous blend.

She sang, her voice harmonizing with the witch's, until, between them, the girls produced a faint, eerie, hair-prickling melody.

But when they each quaff a beer, their voices and lips miraculously harmonize.

Bellisea continues to sing, and Prometeo joins, their voices harmonizing.

The voice and the girlish figure harmonized perfectly and seemed to belong to each other, while the head and face were those of another creature.

Their voices harmonized with the roar of the sea, so that the sea almost drowned them out.

In Nashville, after singing "Long Black Veil", the two first realized that their voices harmonized well and they started to perform as a duo.