[rob74]

Same as the famous discovery of Penicillin in a petri dish contaminated with a mold that killed off the bacteria?

...but now I'm starting to wonder how many people working in a lab didn't clean their hands well, licked their fingers, and died, because they had accidentally discovered a toxin?

[Cthulhu_]

Dying is still a valuable scientific outcome, but few people become famous for it except maybe Marie Curie.

[Eisenstein]

Except it happened to be in a petri dish and it happened to be observed at the time by a scientist. Total accident!

[bregma]

Serendipity favours the prepared mind. That's all.