Lone Island palace treasury

[RenaissanceMan]

Okay.  I cannot for the life of me figure what to do once I get inside the treasury in Amon-Cul's palace.  I know I need to get the dagger, but I can't figure out how to do that.  I've "looked" and "handed" everything in there.  I read the book that's in there, and turned the dais to illuminate various objects in the room and "activated."  The Nautanai effigy made a strange sound when I activated it, and with everything else, the ground shook, but either way, nothing actually happened.  I have the strange key, but it doesn't seem to fit any lock, including the exit door.

Is the solution to this puzzle in this room, i.e. can I figure it out with what I have?  I truly feel like I missed some important information somewhere along the way and now I'm stuck.  Anyone want to offer any subtle hints?

[MusicallyInspired]

No, the sound means you got it right. The shaking screen means you got it wrong. It's a sequence, as Wizard said not so subtly.

There are no dead ends in the game (though, there are deaths, obviously. Some people confuse those). If you're locked in an area of the game everything you need is in that area. No worries.

[MusicallyInspired]

Okay, technically there are are subtle gong sounds ️installed  when you activate the dial's beam at the matching sculptures,

Yes, that's what he was talking about. This is what he said:

"The Nautanai effigy made a strange sound when I activated it, and with everything else, the ground shook,..."

but to hear that properly next to the sound of running water,
a player has to turn down your beautiful music ️️, and who can bring oneself to do THAT ♪♫←?

Hah! You can still hear it, though.

[GameDevChris]

It was the crab that beheaded the previous initiates, as is seen when D'arc loses his battle with it.

Amun-Cul easily allows D'arc to win this fight, as she is very powerful - certainly far more magically experienced that a novice. But she wants him to believe he got the upper hand because smuggling the artifact out of the palace is the only way that she can be freed from her imprisonment.

Why a dagger? Because putting herself at D'arc's mercy will build his trust when seeing her in vulnerable state. The chance of being killed is a calculated risk that she takes. Relying on D'arc's training to kick in and for him to do the moral thing. But either way, through death or otherwise, she still gets a chance to escape her imprisonment.