As she turns and twists the devil's head, Charity finally spins it far enough and is listening closely enough that she hears a different, slightly louder click as she turns it clockwise.
The Grandmaster looks intrigued Robert's request. He thinks for a moment, then nods aquiescence to one of his bodyguards. The half-orc dips out a pitcher of water and hands it to the Ranger.
Gavin's investigations do indeed reveal an aura of magic about this chest, specifically of the Illusion school. As soon as he recognizes the aura, he is able to see through the simple spell . . . the box is actually quite ordinary underneath the spell, and is not even locked.