It's really not much of a problem.
You won't be able to digest it. Your stomach acid will strip away some of the outer metallic shell. It won't split into pieces, if that's your primary concern. It should remain in its approximate state throughout its voyage.
Passing it won't be much of a problem. Your sphincter is much more flexible than your nasal cavity. If you didn't experience any pain during the initial swallowing, you shouldn't have any real discomfort to worry about.
Internal bleeding probably won't be an issue.
If it is, you'll know pretty quickly.
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