Pneumonia is where your alveoli gets filled with a substance causing breathing being difficult. This substance is attributed by germs that gets into your alveoli. Your cilia is supposed to move away mucus ( which traps bacteria ) so when you do acts that causes mucus getting into your trachea ( smoking ) sometimes your cilias don’t move some mucus and that mucus go into your alveoli. Hope this helps. Sorry this is such a long answer I like to give a lot of information
