I found it really interesting to hear researchers speculate about what these drugs actually do and how they do it. The common sense of a mystical/spiritual experience, even among naturalists/atheists, is interesting. And I'd never considered the difficulty of conducting controlled trials (especially double-blind ones!) with psychedelics.

I also learned things I hadn't known about the history of many psychedelics. I had no idea how much study there was into these drugs and how promising they seemed for some ailments before criminalization. I also didn't know Doug Engelbart ("the mother of all demos") took part in the acid tests.