Here is the scene : http://www.youtube.com/watch?v=_kD54-q1uFM
It is right before the final duel and lets the audience know Harmonica's motivation in wanting to kill Frank.
Harmonica's brother is standing on Harmonicas shoulders with a noose around his neck. Harmonica is the only thing keeping him alive. Franks gang are present and knowing that there's no way he can get out of this alive he kicks Harmonica to the ground.
Right before he kicks Harmonica away he says something but we can't hear it. Does anyone know what he says?