Like almonds and peach or apricot pits, manioc root (casava) contains natural cyanide compounds that improper preparation doesn't remove. Shred; squeeze; soak; squeeze; (repeat? Not sure.) dry; powder, grind, or rice; then prepare.
The women may have obtained improperly prepared or contaminated flour.
And to think we had tapioca for desert tonight.
Wouldn't it take a heck of a lot of casava floor to have this level of toxicity?