When you play the song prior to this routine, you will not associate this particular song with that particular person. But since it started playing exactly when you came to realize that you’ve fallen in love, the song now becomes the stimulus that produces the reflex of reenacting the same feeling in your chest when you’re thinking of that special person, which is essentially the same response you first encountered. Prior to conditioning, the Neutral Stimulus (NS) is the song and its playing elicits no emotional response. Unconditioned Stimulus (US), on the other hand, is the moment you fall in love with your special person as it triggers the Unconditioned Response (UR) or the warm feeling you get in your system—the organic and unlearned response of your body. Now, when the classical conditioning is occurring, the NS would not initially elicit any particular response but when forged together with the US, it will automatically trigger the UR. That’s why after conditioning, the Conditioned Stimulus (CS) is still the song but after it had been associated with the experience of falling in love that goes along with the Conditioned Response (CR), which is the warm feeling you get when you hear the song even without the presence of your special person.