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Boat trackers(纤夫qiànfū) refer to those who track or row the boat for others and take it as a profession(a profession is a type of job that requires advanced education or training). When the carrying of a whole set of things such as coal, lumbers, agricultural and sideline products as well as daily commodities greatly relied on water transportation, boat trackers played a key role at that particular time.
They would bend their body and drag the halter through their back with great effort to move along. Apart from tracking the boat, they also chanted the boatman work song with their hoarse voice. The song features no words but the sound like: "hey, hey yo yo, hehey, tuo (meaning dragging) ya, tuo, tuotuotuo ...". Whenever the boat was forging against the current or facing dangerous shoals and waters, it depended a lot on the united efforts of all the boat trackers with their song resounding in the empty valley(a valley is a low stretch of land between hills, especially one that has a river flowing through it).