That's the finger thing from left finger to right finger going back and forth across the board, never touching a number more than once.

在合并时，我的左手手指,和右手手指来回地在黑板上移动，但对每个数字只会碰到一次。

哈佛公开课 - 计算机科学课程节选

I'm gonna use my left finger and my right finger and each of which is gonna point at the start of each of this list.

用我的左手手指和右手手指,每个手指指向每个列表的开始处。

哈佛公开课 - 计算机科学课程节选