And that's the kelp growing vertically downwards.

那就是垂直向下生长的海带。

In Japan, children throw a lower baby tooth up onto the roof so the next tooth grows healthily upwards; an upper tooth goes under the house so the new adult tooth grows downwards.

在日本，孩子会把下齿的乳牙放到房顶上，这样的话下颗牙将会长得结结实实；上齿牙会扔到地上，这让孩子的上齿牙会往下健康地成长。