just remember that you're doing more than just discoloring the lungs. this was actually one of the more memorable experiences from the anatomy class i just finished. they keep big plastic storage boxes of parts from past cadavers, and one of those boxes is full of lungs. healthy lungs were just like sponges, you could squeeze them down easily and they'd
spring right back. smokers' lungs were very stiff from all the tar accumulated. i couldn't squeeze them much at all. and, maybe they're not so stiff when still in a warm, living body, but i can't imagine they'd be easy to breathe with either way.