Ha! Inconceivable!
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In regard to the storytelling part of it, continue the storyline and you may find your answer. I can't really say much more without SPOILERSSSSSSS!
As for poisons in general, I'm pretty sure there are some that have instant effects, even if it is initially just paralysis followed by death soon after.
There was an interesting lore nugget buried in that plot. Dunesfolk have a habit of putting trace amounts of poisons and venoms in their tea so that they build up a tolerance to them. It is a cultural habit that developed due to living in desert regions with high quantities of poisonous animals.