The meaning here is as follows:
Broken hairpin: a metaphor for writing on the corner of a stroke. Take "turn right" as an example. First, the wrist turns to the upper right at the corner. At this time, the pen tube is slightly inclined to the lower left. At the corner, the nib is slightly pressed down, which is convenient for changing the nib, and at the same time, the wrist is turned to the lower left. In this process, the pen is still written by the center, and the strokes should be round and smooth, like Chai Jin, without stagnation. "Turn left" makes sense.
Pat the sand: a metaphor for using a pen in the center. When the cone front cuts into the sand, the sand on both sides will inevitably rise evenly, while the middle is deeply concave into a line; Compared with the middle, the starting and ending shapes of lines have no obvious sharp corners, but are circular. This very accurately reflects the central brushwork of calligraphy and the rich and full images with three-dimensional lines written in this way.
Leak mark: Leak mark is a metaphor of pen, which was put forward by Yan Zhenqing. For example, when painting vertically with a pen, the pen can't flow downwards at once, but must flow downwards suddenly, which makes it vivid and round, so that the pen and ink can be like a leak between the walls of the house and have a dignified and natural shape. Therefore, the realm of "leakage mark" with a pen is higher! The above is for reference.