The list of potential agents in this scenario is small and easily detectable in blood and tissue samples, even if the original carrier has been discarded.

After nine years in poison control I can remember one case in which we were stumped by the agent, an organic phosphate that had been accidentally rebased to have a structure that fooled Mr MassSpec. In all other cases, where there’s effect there’s an agonist or antagonist that can be clearly identified.

The mind is a miraculous place, much can happen in it, even a poisoning.

How do they differentiate between poisoning and psychosomatic panic attack?

"Tingling fingertips" hardly seems like "acute poisoning". And brief chest pain seems more likely to be the result of chest pain.

So "acute poisoning from an unknown substance" seems doubtful to me.

“Acute” is used as in “acute toxicity” versus “chronic toxicity.” Poisoning via one-time exposure, as opposed to, say, a decade of eating lead paint.

I've never heard of someone being poisoned by touching a napkin. Is there some substance that can be absorbed through the skin so quickly? Sounds like something in a murder mystery or sci-fi story.

DMSO is one of those substances. You can dissolve other substances in it and if you apply it on the skin it would go through. It leaves skin very dry and it tingles a lot. You would need to apply water or hydration cream to stop the tingling. But napkin would need to be drenched in it and it would probably evaporate quickly too if left for too long.

DMSO can facilitate the absorption of tranquilizers, poisons, or almost anything if it's the right kind of compound.

If she tasted garlic, it was likely involved.

https://www.webmd.com/vitamins-and-supplements/dmso-uses-and...

Such substances do exist, though they're never as convenient and reliable as mystery writers make them out to be.

In this case, I'd guess that what was on the napkin is "nothing", and her mind does the rest of the work. Though tingling in the fingertips can be produced by a vast array of substances, and my second guess would be "napkin smeared with Ben Gay".

I agree, third might be (alcohol-based) hand sanitizer, which has more of a cooling effect than water when it evaporates, could easily be mistaken for tingles if you're already primed and hyperaware from wondering "did i just touch poison?!". And the acute chest pain seems likely to be a symptom of panicking about being poisoned.

Which "substances"?

Is there some substance that X. The answer is always yes, because he universe is a huuuuuge place. That you fact that you haven't heard of X means precisely zero unless this is your expertise.

Dymethylmercury immediately that pops into my mind

https://en.m.wikipedia.org/wiki/Dimethylmercury

Yeah, but why would a nerve agent or other bio toxic compound be worth putting there? I would them such compounds would provide physical or biochemical evidence, though. Such as pinhole pupils, rigidity or cns depression. Are there “entertainment” compounds that cause tingling as panic might account for the rest. Or something that’s a stimulant. Prank?

Russia has used such things against opponents of Putin. But these kinds of substances are hard to come by.

Speculative. You're more likely to find a 10 ct. diamond than novichok in your entire life.

I think that if you're a Russian dissident the chances are considerably better for Novichok.

Imagine they're common place in texas to go with the guns