I know....
.... this just wants to be a "funny" submission - as you rated it - so I shouldn't be questioning the true facts of life, BUT: when oxygen gets to the lungs, it is acquired by blood vessels and taken throughout the body, while the oxygen that already made it fully through has become carbon dioxide (so there would be two oxygen atoms and a carbon atom) and is realesed.
I was expecting for those particles to take a full tour throughout the body, but this showed me you got tired enough too soon and so a "normal", non-that-funny cartoon resulted from your good graphics efforts.