Households in Amdo traditionally prepare food using iron stoves in low hearths.  In this riddle, the "low end of the valley," references the position of the traditional fireplace stove. A kettle must make contact with this stove to boil water.  Therefore, when the kettle is in the low end of the valley, the water will boil. Eventually, steam built up inside the kettle will be released, resulting in the crying sound described.