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These are great problems! In a couple of my classes, I use collections of problems like these as term projects. I give them different values based upon difficulty, and students choose which ones they want to do. They present their solutions to the class on the last day of the class. Everything is open book, take-home, no time limit. I like this approach because it's more realistic and creative than an exam, there is no time pressure, I don't have to waste class time on exams, and it gives students control of the process.
I was thinking in general terms. The properties of the substance have effects not visible to the eye, and not readily predictable in regards to their effects on human physiology. It was meant to be relatively metaphorical suggestion, just in case science doesn't know everything. So you're right, chemistry says nothing spooky is happening. But there is definitely not enough spook.