Well, I tend to look at it in terms that I can identify with....If you're walking around in a cave or a barn or something, occasionally you get dirt or straw or cobwebs on you and even in your mouth as you breathe. A clam lives in the sand and digs in it, so it would stand to reason that occasionally they might get some in their 'mouth' or lungs (gills). Too much and it could kill ya- or at least make you cough and choke and think you're dying, Eh?
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