所以说虽然舌头仍然触及牙齿，它却是在向后移动。

So though it is still touching the teeth, it comes back like that.

youdao

牙线紧紧地贴着牙齿，往上向远离牙龈的方向移动，再沿着牙齿邻面向下移动，把这个动作跟牙线的前后移动组合在一块。

Hold the floss tightly against the tooth, and move it away from the gum. Slide it firmly down the tooth surface, combining this with a back-and-forth motion.

youdao

比如，你可以从左至右从顶端刷你的牙齿的外面，然后移到里面从右至左。

For example, you can brush the outer sides of your teeth from left to right across the top, then move to the inside and brush right to left.

youdao