A crash in slow motion

I saw something weird at the supermarket about an hour ago. Two old people (quiet at the back!) were pushing their trollies along at a shuffling pace on a clear collision course. They both seemed to have noticed each other but kept shuffling along regardless, getting closer and closer. After nearly a minute of this the two trollies finally collided but with so little force that there was no audible sound. The whole thing was bizarrely hypnotic to watch.