A weird thing which is discussed in the textbook is if you wait a while and then you try it again with the bell after a couple of hours, the saliva comes back.

教材中讨论了一件奇怪的事情,如果你稍等一会,在几个小时之后用铃声重新去尝试，狗会重新开始分泌唾液。

耶鲁公开课 - 心理学导论课程节选