Honestly I don't think about any of those things. I take a deep breath, maybe two or three then slowly exhale until I have pressure in my lungs but oxygen left to stress about having oxygen. (while doing that I am acquiring the target) I have in ear plugs and can hear my heart beating, everything Is set, on target now everything is timing because I have to make my heart skip a beat at the same time the trigger goes off... but this also needs to be a surprise with no movement. It's tricky... But it usually works, I have no clue what my thumb is doing.