...Actually, just a list of good, archaic poisons would be great.
Okay, I'm writing a Rurouni Kenshin fic. And I have this group of say four gaijin men (Americans in specific). They're staying at the Aoiya. They've been really horribly inconsiderate. Taking up the common room for gambling, being loud, being abrasive, expecting better service. The last straw is when they ask for coffee in the mornings instead of tea, and Shiro and Kuro oblige.
Misao takes a little of their coffee and calls it "inconsiderate jerkface tax". This pisses the Americans off, as those were their coffee beans.
An hour later, four American men are facedown in their food, dead.
Misao, on the other hand, is having a seizure. And also survives.
What would fell four big strong American men but leave a sixteen year old SHORT Japanese girl alive and kicking? Even if she didn't have half as much as they did.
The seizure thing isn't all that important, but I want it to be obvious that something is wrong with her without too much grossness. No hacking up blood (sigh), vomiting, loss of control of bowels, or outright death. She needs to be very much alive, and very obviously DEATHLY ILL. Her being not all-there-in-the-head would be nice, but not totally necessary.