...are certainly not silly (ugh).
Probably evolved from a symbiotic prokaryote, ciliated cells line the respiratory tract from the larynx on down, and sweep foreign material "upward", away from the delicate alveoli. An interesting fact is that in three dimensions the cilia "change the direction" of their motion so as to keep the material moving toward the pharynx.
Cigarette smoke kills cilia, ultimately allowing "gunk" to slide into the terminal air sacs and rot there--leading to emphysema, chronic bronchitis, and cancer. Just one more way smoking kills.
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