Hello Andrei, Thank you for shedding light on this most peculiar detail in a fresco! Those who follow the History Channel's Ancient Aliens program will be familiar with it.

The opacity of this detail may soon be clarified because “When President Donald Trump signed the $2.3 trillion coronavirus relief and government funding bill into law in December, so began the 180-day countdown for US intelligence agencies to tell Congress what they know about UFOs.” (https://www.cnn.com/2021/01/10/us/ufo-report-emergency-relief-bill-trnd/index.html)

That announcement, depending on what is disclosed, may end up being the highlight of this year (as if there wasn’t enough excitement in the world already!).