"Shell" is often slang for money. "Shell out" is to pay money for something. ... .... Somewhere (can't locate it now) I have a cute little box of small conch shells used in many places for gambling chips. The printing on the box notes that use..... Anyway, here is what they look like. The small shells are 0.8 centimeter (less than a half inch). Snails once lived in them:

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GaryCooper