....then why doesn't spiral zetsu know about poop? Plot hole or no?
If not a plot hole, please explain the reason in detail.
Could it be that the victims of the first IT weren't necessarily humans?
Zetsus have zero memories of their pre IT forms. They are complete shells of their former self.
Zetsu knows about poop. It just has never felt the sensation of poop.
So to illustrate this a bit better.
Kiba is stuck in IT.
He never leaves it.
Over time his mind leaves his body behind, and just stays in a dreamlike state.
Over time his body transforms into becoming a zetsu.
Kiba is now a zetsu.
Kiba now no longer kiba. Zetsu retains no memories of being kiba, and does not retain any part of kiba at all. He is a completely new being, created out of the living remains of another.
If you are looking for a plot hole, a better place to start, would be to study about how tobi was able to create a zetsu army, without stealing 100,000 people.