Another guy's perspective...I also look at my nails, though most often the cuticles. Sometimes they turn red, or bleed when they crack. I used to keep the nails short for my martial arts, but with the Iaido, I don't have to keep them as short, but still look at them.
As for breathing, That is something I noticed when I was practicing my Iaido on film. It didn't look so good the way I was doing it, so I tried to change my breathing habit, and breathing is essential for ANY martial art, anyway. The breathing happened to be when I got a little nervous, and so I worked on being aware of it at other times.
Also, did anyone know that yawning is actually a method of resetting the breathing pattern? I heard that while I was practicing karate, and I think it would mostly occur when my breathing was too shallow after a workout, when it should be more deeper.
Since I no longer got my hands tarnished from work, I was contemplating on getting a manicure, but decided against it, despite the fact I do have occasional cracking and whiting of my nails.
BTW, I get a LOT of comments here about how big my fingernails are, and only the doctors are aware of why they are clubbed. However, my wife said the cutest thing one time, she thought my fingers looked like "Space Men", so I would tease her about it, and do things like; as I would wave, I'd say "Spaceman Five!"