When people speak of poison, the same general image gets conjured: a vial of flask filled with a green liquid, possibly bubbling, and occasionally with a skull and crossbones label.
The effects of poison are similarly uniform. Fast-acting poisons cause the victim to clutch their chest, fall down, and die. Slow-acting poisons cause headaches, deathly pallor, and eventually bed-ridden death.
I find it amusing when people talk about generic poison, but also a little sad. At some point, the inquisitive mind should wonder what "poison" is, exactly. It should discover that "poison" is a general term for a substance that causes harm or death, and should discover that the number of substances out there that can do that, as well as the number of ways that they can cause harm or death, is tremendous.
I find that people who write about generic poison are about as amateur as antagonists who want to rule the world. Both should only be used when making purposely simplistic stories, and neither should be taken particularly seriously.
If you never have thought about poison before, then consider this an example of common things that people overlook. Also consider it a challenge to ponder other classic tropes in writing and see what else you may have missed.