I've seen the survival of some of their subtle poisons.

The effects of the subtle poison would not be obvious for at least two days, when the unfortunate nay-sayers were well on their journey home.

I must find this subtle poison which was strong enough to undo the elixir.

Who would ever suspect a subtle poison had been slipped into mother's milk?

And if they were some subtle poison, why had she waited so long to flee?

Could this air here, which our ship's instruments tells us is good, be some kind of subtle poison?

Such subtle poison might work at the Top of the Beyond, but not down here.

Good clean water, faintly sweet; but with what subtle poisons?

There were poisons so subtle that to know their properties one had to sicken of them.

As scientists learn about the delayed effects of more subtle poisons, regulators face much harder judgment calls.