Here's a true story. A few years ago, I was in London at a tube station. It was one of those with an office in the middle of the platform - I was probably 20 to 30 metres from the office.
With nothing much else to do, I was watching a lively discussion going on through the office window. I was much too far away to see faces, but lively was certainly the word.
Now here's the thing. I recognized one of the people in there, simply from the way he was moving. There were no contextual clues - this was someone I hadn't met for about 5 years, who had nothing to do with London Underground, or even central London in my mind. But I knew it was him. And when he came out, it was. He had been having an argument with the staff over something.
So, why could I recognize this one person? A (as I shall call him) has a stunningly distinctive pattern of movement. It couldn't have been anyone else. Now, I'm not very good at recognizing people, in part due to short-sightedness and in part due to a tendency not to look at the faces of people I don't know well. But this was clear recognition.
It made me wonder why so few people have distinctive movements - but a few do. I suspect a good bit of pattern recognition software would say we were all distinctive. Fascinating.
(Why five barred gait? I couldn't think of a better pun. And we used to stop at a pub called The Five Barred Gate on the coach when my grandma used to take me to Blackpool Illuminations as a child - but that's a different story for a different day.)