Comment by tyrabound

Decently intentional and deliberate in many if not most cases. There are examples of it in high up places along sheer cliff walls in Arizona that boggle the mind trying to figure out how they managed to accomplish it and at the scale they are, then there are cave paintings that are hundreds of meters deep inside narrow caves in Europe.

It actually makes me wonder if this technique would produce any results in the notorious Erdstalls in Germany. I suspect not, but no one has any better ideas, so it might be worth checking.