解説FastCCI Commons gadget showing why a file is erroneously categorized into a category (category-tree).png
English: FastCCI gadget showing the source of a category of a file that was erroneously categorized into a category.
I did this and used the gadget to correct error by clicking the FastCCI dropdown button on the top right of a category page and selecting "Quality images". From there I opened this image which seemed misplaced to be located anywhere underneath "Category:Microscopic images relating to biology".
The flaw was that "Category:ABO blood group system" was categorized into "Category:AB letter combinations"; also not all files/subcats in "Animal cells" are microscope images.