It says you are on the ground on two occasions.

在两个点你是在地面上的

耶鲁公开课 - 基础物理课程节选

Now, I've talked about laughter on two separate occasions and on each of the occasions when I talked in front of a large group like this somebody came up to me afterwards and said, "But I can."

我之前也有两次提到过笑,第一次,当我在这么一大群人面前讲完后,都会有人上来跟我说，“我可以”

耶鲁公开课 - 心理学导论课程节选