I think they might mean the creation process for Gu [1], which apparently involves sealing several venomous creatures in a jar together and then extracting pois

I think they might mean the creation process for Gu [1], which apparently involves sealing several venomous creatures in a jar together and then extracting poison from the last survivor. [1] https://en.wikipedia.org/wiki/Gu_(poison) https://en.wikipedia.org/wiki/Gu_(poison)