People Watching at the train station

Today, I took the train to Toronto on the way to my folk's place and had some time to kill while waiting for the next train. I decided to pass the time by doing some people watching. Off in one corner were two women with two kids. The youngest was wearing a harness which was attached to her mother by a long stretch cord. The energetic daughter could pull all she wanted by was constrained by the stretch cord. This kid was a bundle of energy. I started to wonder about the durability of the stretch cord as it getting a real beating. I came up with some estimates as to how long it would last and surmised as to what might happen at a critical moment. I didn't have to wait long. Just as she was darting towards a sofa, it happened and she fly into the sofa. Mom wasn't too surprised as she opened her purse and started to unravel a new stretch cord. Happily, the daughter got up and started to pull away as she was attached to a new cord. I started to wonder how many stretch cords the mother might have in reserve but they were calling my train at this point.