I'll freely admit not knowing how 40k daemons work, but I don't think we're much like a possessed person. For one thing, we haven't gone on any rampages or anything.
Attempt to incite a riot for fun and profit says hi. Plan to set fire to the town for fun and profit says hi. Theft of large sums of money from civilians says hi.
And yet, much of the town is unaware of us. I think a proper rampage would involve more, y'know, rampaging.
And that says more about Bay12 than the familiar.
While we're on the subject of 40k...remember why the young Techpriests (or whatever they're called) are the conservative ones? They don't live to be old.
Wat?
I read somewhere or another that...Inquisitors, maybe?...some Imperial position, the young ones stick to the book and the older ones tend to be more liberal. The explanation basically boils down to non-hereditary natural selection.