at the 14th second, the video shows something like a hammer, https://youtu.be/nJgD6gyi0Wk?t=14 https://youtu.be/nJgD6gyi0Wk?t=14 I don't understand it. the ham

at the 14th second, the video shows something like a hammer, https://youtu.be/nJgD6gyi0Wk?t=14 https://youtu.be/nJgD6gyi0Wk?t=14 I don't understand it. the hammer seems to ram down wooden pillar at the same location. I think for it to work, the hammer needs to move around the wooden rail .