A Conditioned Emotional Response (CER) is a learned emotional reaction in response to a stimulus. For example, the smell of mothballs (which is a neutral stimulus) may remind you of playing hide and seek at an aunt’s house when growing up (which is associated with positive emotions). Now when you smell mothballs, you feel happy.
Lots of dogs develop CER’s to different stimuli. How many people have had a dog who runs away when they see a hairbrush, or backs away from a collar?
You can help your puppy build positive conditioned emotional responses to things like nail trimmers, harnesses, or ear cleaner.