Paul was late. When he entered the room his teachers sat waiting for him.

VOA: special.2009.04.04

But Pavlov observed that when somebody entered the room who typically gave him the food powder, the dog--the food powder saliva would start to come out.

他注意到,当给它喂食的人,进屋时，狗便开始分泌唾液。

耶鲁公开课 - 心理学导论课程节选