The one-way rocking motion of the ink blotter is exactly the way how our front foot grabs the floor after shovelling out, in order to pull the rest of the body forward. The rear foot performs the follow step as the body is pulled forward. The upper body has no movement and is sitting every still on top of the lower body. The overall forward movement looks like a crab walk or someone sitting in a car with the wheels spinning and making contact with the ground driving the car forward. The body of the car sits on a solid platform. Our platform is the dang (two knees and the groin), which structure must remain solid while we move forward. What below the knees are the only things allowed to move. The halfpipe shape of an ink blotter is opposite to how our foot looks, yet when it rolls forward, it represents how our toes press down to the floor to create the initial lever action in the foot to pull the body forward. When someone uses an ink plotter, he/she will likely rock it back and forth. This is not the way our action is like. If we do so, it is equivalent to that we have done nothing. We have to think of the ink blotter as a little boat and how it move across the table. It requires us to first put the rear end of the ink blotter down to touch the table while the front and middle parts are off the table. As we press down on the front end, the bottom of the ink blotter will progressively touch the table, after this pass is complete, the front end will be touching the table, at this time, we need to quickly switch back to have the rear end touching the same spot of the table, and repeat this action. The overall effect is like a little boat riding on a wave being push forward. This is also another example for our worm action.
This action is described in detail by Master Chen Zhonghua in this video: