Nail in my sea strainer

Prior to departing yesterday, my wife and I were going through our pre-departure checklist. Checking the strainer for debris is top on the list. I pulled the stainless steel basket from my Perko strainer and found a rusty finishing nail!

I spent several hours trying to figure out how a nail was sucked up into my vessel. I have a clam shell strainer in addition to the Perko strainer. I haven't run aground or hit any under water objects. Perhaps I churned up some mud and a nail on the bottom was sucked up?

Bizarre...

Diver with a twisted sense of humour?

I have heard of people putting solid copper wire in the baskets to help slow hard growth.

Found a letter once, no metal bits.