Here's one I just thought up.

Why does marijuana produce THC? I don't think THC carries out any vital functions in the plant, so why would it waste energy on making it? It would be more reasonable if THC was a poison or something so if a cow ate it, it would be like "not gonna do that shit again," like with loco weed. I heard somewhere that a lot of animals don't even have THC receptors, so it seems to me like THC is to marijuana as tailbones are to humans. I guess we just caught a lucky break with THC!

Also, who decided to go smoke every plant he saw to see what happened?

I wonder what it was like for the first Indian who are like 2 lbs of shrooms because he thought he had himself a tasty meal?