I watched, amazed at her lithe dancer's step, till she dumped her tray and glided through the back door, faster than I would have thought possible.

我吃惊地看着她那柔软灵活的舞步，直到她把自己的盘子倒掉，然后悄悄地从后门溜了出去，速度快得超出了我的想象。