When living in university halls of residence, I could identify each of the thirteen residents of my block by their footfall along the corridor outside my room. Training was entirely subconscious. Validation was easy, because people would often walk along a bit before greeting someone or talking to themselves.<p>There are all kinds of reasons someone might change their footsteps based on health or what they're carrying, but most of the time people probably walk in their own characteristic way. It's a shame that the panopticon is always creeping in on us, but in this modern world, it's easy to imagine footsteps being used for security, to flag someone for review that they may not be who they are presenting as being.