Here’s a puzzle; maybe some of my readers can figure it out.

My wife showed me a tiny pinhole that appeared in one of our stainless steel pots. How did this happen? What mechanism could have created the hole?

I took one look and said “cosmic ray hit”. But I was joking.

The pot is a few years old, but has never been used for anything unusual – just a little cooking and storage of food in a fridge.

The hole is just above the penny – you can see the light shining thru it (click on the image for a larger version).

It’s fairly thin steel; about half a millimeter.

Here’s a close-up photo of the hole from the inside:

The hole is about 0.2 millimeters in diameter (the crater is larger).

Here it is from the outside:

So it looks like whatever happened started from the inside.

What did happen?