Classical conditioning is used a lot when training animals. Rewarding desirable behaviors and punishing undesirable behaviors enables pets to learn how you want them to behave, or maybe just whatever gets them a treat. I have used techniques like this with both my dog and two cats. One of my favorite things I conditioned my dog to do was to ring a bell with her nose whenever she wants/needs to go outside. This was so that if she went to the door to go out when we were in another part of the house, we could at least hear her and come to let her out. It only took a day or two to get her to understand the concept. We kept an eye on her and whenever she went to the door we followed her and put the bell up to her nose making a the sound. We then would try and get her to repeat the movement herself and would reward her with a treat before opening the door. Ten years later and we still hear a bell ring and know she needs to go outside to go to the bathroom. Bells are a common tool for conditioning; the sound can be taught to be associated with many different things. I learned from this post that teaching dogs to ring a bell to signal they have to go outside is actually very common. I attached a link below.