The Man Who Bit a Fell-Beast

[Rune Son of Bjarne]

I never read is as an evil conjured up by Sauron. I think the reason for this is fairly simple. 1) Tolkien never states that it is created by Sauron (or anyone for that matter) and 2) It seems to be a one off thing in the third age.

Continuing from the second point, if you developed chemical warfare (or improved on it, as Melkor appears to be the creator), and it had the desired effect. Why on middle-earth would you limit your self to one go? Surely you could perfect it, or make it even more precise in targeting exactly the creatures you want to rid your self off.