...after watching POC 4: Stranger Tides.
Poisons can be used to amplify the effects of all bladed or semi-bladed melee weapons. Applying poison to a blade will give it said poison effect in percentile form. Naturally, every time the blade is used the percentile goes down. The higher the percentile, the higher chance of poisoning something when you strike at it. Poisoning something is never a 100% guarantee, however, to prevent there from being way too easy hunting (yes, it'd work on animals). Poison would work the same as rattler poison does already, slowly decreasing humors until whatever it is you poisoned dies. There could be different types of poison that could decrease different humors. Naturally, this'd be a thing for potion makers. This would also give people more of a reason to have anti-toxins handy.