Tales written in sand
When I was a kid I learned how to track as a matter of course. Most everyone had at least the basic skills where I grew up, some were better, some were worse, I was somewhere in the middle. (still am as best as I can tell)
The track and sign left by an animal or a person can allow you to read their condition, their level of fatigue, how quickly they are traveling as well as a number of other things.
Looking at my own tracks is something I often do for myself, being as it is one of the few ways to get feedback on my own running technique without someone coaching me. There is nothing like looking at your own tracks to tell you if you are running as well as you think you are.
I also do this with the people I work with. I take them to a convenient sand lot and have them walk and/or run across the sand. This allows me to study the tracks they leave and gain much more information about their walking/running technique than I can tell just from watching them run. I have to admit, it can get me some interesting looks from time to time. To really study a track you often need to get down on your belly and move around the track in a 360 degree circle in order to see all the nuances.
Reading someone's tracks can be a really valuable tool for learning how they are doing things that may be contributing to various problems. If someone comes to me complaining of back, hip or knee pain, whatever is causing this will be reflected in their tracks. Often it's the easiest way to discover how they are doing their discomfort and to see the changes that will help correct the problem.
The key is what's called pressure releases. A pressure release happens as the foot pushes off against the ground. Pressure releases will tell you where and how hard a person is pushing off with each foot.
Here is an example from one of my own tracks.
We see a good forefoot strike, with the leading edge of the heel just touching the ground (I'm wearing my trail running shows so I can make a good impression, no pun intended) only the first two lugs on the heel are visible. This means that the only heel contact was from absorption as the Achilles tendon stretched from the energy of the foot strike. There is a slight pressure release in the area of the third, fourth and fifth toes (upper left corner of the track) This indicates that I took off with more weight on the outside of my foot. I suspect tension in the foot as the cause, giving me a slight twist at take-off, or not allowing full pronation on landing. The latter seems the most likely as the track is not as deep at the big toe. I need to pay attention to this.
Here's another track from one of my students. Notice the deep pressure release at the outside forefoot. What would be a possible cause for such a movement of the foot?
The trick is, of course, to imagine how a foot would have to move to make that release, and under what circumstances it would do so.
There are some good resources to learn the rudiments of reading tracks out there. What you want is something beyond just identifying a track. A good place to start might be with the book "Tracking: a blueprint for learning how" by Jack Kearney