I don't recall having read Dunbar, and I'm struggling to remember where I read this, but...
I've got a decent little library of indigenous American material at home. A lot of it focuses on Northern Cheyenne, Arapaho or what we might broadly call 'Sioux', so my guess is this relates to them, but...yeah...can't remember, sadly.
Anyway...there were descriptions of a process used when encountering unfamiliar berries or fruits. Effectively it involved checking the actions of local animals, particularly birds, before ingesting a small amount, rubbing some juice on their arm, and a few similar, small-scale actions.
This would be followed by one person ingesting a larger amount.
Once the berries or fruit was 'approved' it could be more generally consumed.
This isn't exactly scientific method, but it's a methodology of some description. I remember at the time being frustrated because there was no mention of medicinal plants, or what process was used to identify those, or test them, but to be fair the book was an old one, focused more on first hand accounts than organised research.