I dare say the word "soul". Uh oh, how unscientific of me.
I have no problem with the word soul. After all, it represents the essence of humans that science can't really measure, and probably will never be able to measure.
I was only providing the scientific explanations for a certain phenomenon. I'm not a rabid STEM guy, just a person concerned with science's flawed public image.
As long as you're not giving a "physical" thing an unscientific explanation, then you're golden.