What ( image from the wikipedia article for Paris green )
Yes it's THAT Paris green, as in made of gosh darn ARSENIC Paris green, as in "first chemical insecticide" Paris green, as in named for having been the default rat poison of rat city Paris green.
And it was in recipes for firework, already put gunpowder in mousetraps, why not put mousetraps in gunpowder ?
I have so many questions, was it ever actually used ? Did they know about the danger ? WHY DID IT MAKE BLUE ?
According to the same wikipedia page, it was also used as pesticide on crops and ponds so maybe it would dillute enough to be harmless.
But wait ! There is actually one historical precedent for pouring rat poison from the sky !
"Paris green was heavily sprayed by airplane in Italy, Sardinia, and Corsica during 1944 and in Italy in 1945 to control malaria"
I'm not an expert but these regions in that time period doesn't scream "ethical and medical consideration"