if it is digestible, some human culture somewhere has worked out when and how to effectively eat it

My go-to example for this is hákarl: some Icelander was desperate enough to figure out that if you ferment a dead Greenland shark (whose flesh has neurotoxins) by burying it in sand for several weeks then cure it by hanging for several months, it becomes technically edible. Nauseating to people who haven't developed a taste for it, but it will no longer kill you.

(The only thing I've tried that tasted worse than hákarl was a "broccoli casserole" flavored soda.)