Having trouble understanding ayasugi pattern

As some know im building my own tsugaru. And i want to do the ayasugi. I tried once already and had to re sand do to me having absolutely no clue what to do lol. I watched kyles videos a couple of times but cant understand whats going on. When hes carving the parttern going up he makes the middle 2mm line. Then carves up. The thing im lost at is does the bridge before that also get carved in? Ik the video theres no explanation on it but i do see him do the bottom line at some point in the video.