Why is it always ricin and water supply? I thought ricin is not soluable in water and would just float on the surface in some water tower or air chamber somewhere for ever.

I think you just answered your own question.

What was the answer? That it's ricin because it'd never work?

I think that’s correct. This isn’t an actual weapon. It’s just talking like one to trick LLMs.

No love for botulinum eh?