Poison

Pufferfish venom blocks sodium channels in nerves, while monkshood venom activates them. Because the two poisons work in opposite ways, taking them together delays their effects. In 1986, a murderer in Japan exploited this principle to delay the time of death and fabricate an alibi.

Paris Green, an 18th-century pigment, became popular in Europe. It even repelled insects when painted on walls. But its ingredient, arsenic, killed many before it was banned. The convention of depicting poison as green may originate from this deadly pigment.