Thinking of chemistry. Not in the scientific sense, more in the sense of "the elements that make up something," or "interaction of one personality with another."
Sometimes chemistry is almost invisible, especially when it's working well. You really notice "bad" chemistry, when things aren't working, or when an element sort of "poisons the well." I recently had a deadly encounter with a certain personality. One brief, off the cuff conversation was like "death on a stick." I couldn't extricate myself fast enough.
And that "badness" hung over me like a black cloud for days afterward. There is a real, deadly, overwhelming power there, almost unacknowledged. They used to say... "better living with chemistry," and then there's the other kind... when bad chemistry makes living a little bit harder.