About the year 1995, Matsumoto found these markings while looking for micro ball lightning plasmoids. He said that little micro ball lightnings that he could see would leave the electrode he used, go out of the water, and hit the acrylite film he was using to detect these objects as well as any particle tracks. He used a special micro telescope to see them move.
One or more left his electrode, if I understand what this picture is correctly, and left this hexagonal plate. It was actually a plate, not a hole in the film. He gave me permission to post his pictures long ago, so I wanted to post this. He did excellent work back in the early and middle 1990s that I want remembered. I want to thank Lutz Jaitner for finding this picture. I sought for it for a long time. I think this is an extremely important micro ball lightning mark.