notice the small dark smudges on the lid and right in front of the airpods
My airpod case has magnets in it that keep it closed. These images show the erosion from opening and closing the case for a couple of years now.
Above shows metal shavings that are attracted to the magnet. I can sweep those away with my finger....
but with erosion like this, I can't just clean it away.
You can see some metal pieces in these holes that have worn away at the plastic and caused the erosion. It's amazing what you can see under a microscope!