Direct contact with the Shadow Sand Dust.
Of course Amber wasn't doing this just because her brain short-circuited for a moment. Her personality might be all mischief and bouncing off the walls most days, but her talent for chickening out is even more outrageous than anyone suspects; "cherish life and stay away from danger" has been her survival creed for many years—if she doesn't have at least some confidence, she would never casually touch this kind of thing with completely unknown origins.
Other people had already come into contact with this Shadow Sand Dust. Whether it was Modir himself, who first brought it out, or Victoria Wilder and Maji, who later took charge of collecting and transporting the samples, they had all handled this sand, and none of them showed any abnormalities afterward. Fact was, even though this stuff might be connected to the gods, it didn't seem to harm ordinary people the way other divine relics did. Just touching it should be no big deal.
