Monsters origin?

[Kein]

http://www.youtube.com/watch?v=zmXWI-Lhu6M

I'd liek to talk about monsters existence in Amnesia. Yes, why so surprised? I doubt it, indeed -- just watch the video.

Now, there is few questions pop ups: what prisoner saw in that man?
And why monsters SUDDENLY appear or disappear without an trace? Or why you can't be killed at all, and when you woke up - there is no monsters. Or why neither Agrippa (when you first time meet him or any other time when you "talk" with him) or Alexander (in a prison when some monster brought you there) even mentioned those monsters? May be they (the monsters) exist only in Daniel's mind which full of madness? Agrippa mentioned that even broken Orb "leak madness", so, may be Daniel was way to long under that effect and it made him crazy. Or, it made him easy to be deluded by Alexander's skills (as we know he really has some), and all those monster just an illusion made by Alexander's mind in order to confuse, stop intruders/Daniel. Or may be they are really humans, but Daniel see them as a monster affected by Alexander's powers.

And yes, I know that there is a moment in the game where we feed some meal to invisible monster, but hat hardly works as a support thesis for real monsters existence, since that invisible enemy is.. invisible. Do he really exist?

Many theories and no answer. Your suggestions?