Step into Ivan Pavlov’s lab and run the experiment yourself. First, see the natural reflex. Then pair the bell with food again and again, until the dog drools at the bell alone. That is a brand-new conditioned response. Ring the bell with no food and watch the response extinguish. Then let the dog rest, and see spontaneous recovery. You can also test a similar tone to see generalization. Every stimulus and response is labeled as you go.