The wobble is primarily a back and forth motion for the globe, but takes the form of a Figure 8, well documented since 2003.

而地球的摆动主要是地球来回运动造成的，但是采取的是这种形式Figure 8，自从2003年就被记录了。

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When sound waves enter the cochlea, which is really a tube coiled around, they set a membrane into a back and forth motion and cause a new wave.

当声波进入耳蜗这条盘旋的管道，它令薄膜前后移动并且产生新的波动。

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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.

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。

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For the moment, the back-and-forth motion is occurring as the market continually tries to gauge how the European debt saga will play out.

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