It doesn't just have to be slave labor.   Any repetitive work can inspire song -- hence the Scottish traditional wauking songs, sung by women beating new woven cloth to shrink it down to size.    Ironically, music that used to make work more bearable can also make us forget the whole point of the thing. I'll never forget a "wauking workshop" where we sang Gallic wauking songs and rhythmically tugged on a lovely wool cloth (woven by one of the group). Indeed we carried on so enthusiastically that we over-shrank the cloth, effectively ruining it for further use...