They mention the toxin comes from the rhododendron flower. I remember camping in North Carolina once and one of the people I was with warned against burning anything from the rhododendron in the area, as supposedly the smoke would give you the runs.

I mostly thought they were joking, and I have no idea what specific type of rhododendron would be there (if any), but maybe there’s a glimmer of merit to it? Or maybe they were thinking of a different plant?

This was somewhere in the Blue Ridge Mountains, if I remember correctly.