@Svelandria I'm guessing something like cyanide... he mentioned it was made of "almonds"(cyanide is supposed to taste/smell like bitter almonds, or so I'm told) and she literally mentioned amygdalin(had to look that one up).
@Greyvenn I wasn't aware that cyanide supposedly tastes like almonds. Now it makes sense why our ML reacted when she said almonds and amygdalin. As for why I thought mercury, if my information is correct cinnabar is basically mercury in solid/crystallized form. Or, as our heroine put, stone form when she said "stone cinnabar." Of course, maybe "stone cinnabar" is something entirely separate from the actual cinnabar crystal, but when I looked up "stone cinnabar" just to check my facts all I got was the crystal.