The interesting thing that isn’t usually an issue with tox screens is the they are limited. You can search whole classes or drugs, but ultimately a truly novel poison would be detectable in principle, but likely to go unnoticed. Now for you and me that’s enough, because we have the resources of individuals, but a large lab and especially a government can afford to engineer toxins that are not tested yet.

Having said that, such a toxin that could also be frozen and the resulting “dart” being strong enough to survive being fired into someone, is not perfect. Like the poison umbrella, you’d expect traces of toxin to be found around the wound, and even small wounds become evident under ALS.