I'm a people watcher. I go to events and I end up watching the people just as much if not more than the event. So, I tend to notice little things that might go unnoticed by the passing glance.
When I was in Jr.High/High School, I started developing knee problems from basketball injuries. My mom took me to a doctor who evaluated my walking. He pointed out that at that time, I turned my feet out to walk (toes going out). This could cause all sorts of problems with my knees, ankles, back, etc. So, rather than spring for the orthopedic shoes (thank you, mom!), we agreed to watch how I walked and work on it.
Now, I notice so often people walking that same way and I always want to stop them and ask if they have knee, ankle, back, etc. issues and let them know to change their walking stance.
But then again, I may just get punched in the nose. I'll just stick with watching for now!