Ivan Pavlov was a Russian physiologist. During his studies, he observed that dogs would begin to salivate whenever an assistant entered the room, even if no food was present. Pavlov realized that the dogs had learned to associate the presence of the assistant with the arrival of food. He then conducted experiments where he would ring a bell or sound a metronome immediately before presenting the dogs with food. Over time, the dogs learned to associate the sound with the food, and would begin to salivate in response to the sound alone, even without the presence of food. This research on dogs became an iconic example of classical conditioning and the comic references this.