Note that different people have different research approaches. The two old ladies check that none of them can see herself and the problem is solved! ;-)
The other older lady makes an experiment with motion and rigorously determines that she is ... well ... unsichtbar. :-)
Messier Monday: A Titan in a Teapot, M69 (Synopsis) - “Ancients knew that you need guidance, patronage and protection as you move from one place or state to another, whenever you cross a bridge.” -Richard Rohr...
8 hours ago