If you've ever been using some program, you did something completely innocuous, pull something down from a menu, click a button, you didn't do anything wrong and yet all of a sudden the thing just starts hanging there or you get a little spinning beach ball or the hour glass or whatever it is.

如果你之前在用一些程序，做一些无伤大雅的事情，拉下一个菜单，点击一个按钮，你没有做任何错误的事情,突然间有东西开始一直运行,或者一个沙滩上的小球旋转,或滴漏或是别的什么。

哈佛公开课 - 计算机科学课程节选