Many people that tried Ayahuasca (that turn up the levels of DMT that is one of the keys of the spiritual world) said to seen things like by these entities so when i said that they can possess you trought your anus it was to read litteraly. I wasn't only trying to make you laugh (without success) But Ayahuasca is mostly a mainstream things. Castaneda and Steiner already explained that these worlds (astral and aetheric) can be opened without external help.
How to know if you are possesed? Real question, I've had people trying to demostrate with some weird rituals that I'm possesed by demons and they panicked and I was like "wtf this is nonsense", also had my fair share of wandering around those realms as an idiotic unaware of what I was doing, and had encounter both good healing stuff and dark stuff that made me panic, like shadows trying to catch me and such...
and these entities are parasites. Which you can protect yourself against. Yep astral travel, projection, to the abyss, void, etc. is mainstream. I know all of this. These are beginner topics. Are you a shaman? Yeah I guess you're right. In this thread there are mostly beginners so no point resurrecting it.