Tian Qiu Xin used to recite the following verses:
Since the beginning movement the spiral rises, and the force comes from the feet.
One after the other it passes through all joints, therefore all the body being a unity.
The belly is like the sea, and the form like the tide. When changing the movement, folding comes from the waist.
Although forwards and backwards the level changes, you must keep stability. Upwards and downwards go through each other, and then the force reaches the extremes.
Thanks to John Vanko for submitting this quotation.