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

If you've ever noticed, Mac OS has its Apple menu on the top left and Windows has its start menu in the bottom left, really for no compelling reason.

如果你注意到，你会发现，Mac操作系统,在其左上角是Apple菜单，Windows却把它的开始菜单,放在左下角，毫无理由可言。

哈佛公开课 - 计算机科学课程节选