What is the most interesting Pavlovian experience you’ve witnessed?

For example mine happened throughout grade school (K-8th). I (f20) went to a private Catholic grade school with a total of 120 kids with about 12-20 kids in each class. In kindergarten, my teacher had a service bell on her desk. Whenever she wanted to get our attention, she would tap the bell and everyone would settle down. I remember when she explained it to us on the first day. She said “when I ring this bell, everyone needs to be quiet”. I didn’t realize how triggering that bell was until I got to 8th grade. In 8th grade, two kids are assigned every week to watch over and play with the kindergartners at recess time. I was finally assigned one week with a friend. One day all of the kids were playing like normal and were a bit loud and rowdy. Then one of the kindergarteners went up to the teacher’s desk and rang the bell for fun. All the sudden, ALL of the kids stopped what they were doing, and looked towards the desk. The room was dead silent. All of them had blank faces. I was definitely taken aback by this. Then everyone just looked at each other after a few seconds and then continued playing like normal. Then ten minutes later, a kid rings the bell again. Once again, everyone stops and looks at the desk. This was absolutely remarkable!