[dtvmcdonald]

Originally Posted by Yamamaya42

WHY, is unknown
https://en.wikipedia.org/wiki/Whisker_(metallurgy)

once you get them they don't go away.

you got to scrape and clean them out, and try to paint and/or polish the metal to try and stop it from coming back

Silver whiskers and tendrals (like grapvine) can grow grow to many inches long and many millimeters in diameter. This is slow at room temperature but speeds up at a couple of hundred degrees C and the presence of sulfur.
Natural occurrences can generate specimens a foot high that sell for over $100,000. So can fakes. (OOPS!) The natural ones an grow is less than "geological time" and the fakes in months.