Some instinct had startled them, and they turned their backs on the train and began to bounce away through the grass, their motion as graceful as any ballerina's.
可能是受到了惊吓，它们转身在草原上奔跑，动作像芭蕾舞演员那样优雅。
2
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.