I decided to post this one cause its the third one I have found I will look for other two I saved. I don't know if it means anything besides it being air or gas. so let me know or not lol thanks.
Looks like Gas Start of the problem Zinc Riot, I see the Trail of more Gas problems over at the O so spend it.
I say Gas Bubble also. If you find the other 2 coins with the same exact problem that would be really something.
I think it's a cool coin and I'd keep it if I found it. To be sure, once you find the others, you could poke it with a toothpick/qtip and see what happens.