I don't know.
I never thought that in moderns days (like where we're living in right now), when someone looks sick but the doctor cannot cure or find the cause of it, people would still think (or rather conclude a diagnosis) that there is something inside him/her.
I am not a doctor, and neither do the people who has been doing the spiritual diagnosis, but I can't see where the logic is. We are not living in the past. If we cannot get the answer from a doctor, we have the internet.
Those people in the-not-so-modern days did not have access to the lowest level of (any) information. Imagine, living in a rural area, without highways, without cars, without electricity, without TV & Radio, and most importantly without books. Where do you think they could get any information from? Certainly from the word of mouth. And you know how it works, don't you - I am pretty sure that most of us had at least once played the message relaying game. For some reason, we (well, at least I) would never get the EXACT sentence at the end of the game.
Have you ever thought why people say that when a baby starts playing with his saliva, the mother will start losing a lot of hair? Or, when a baby can touch her mouth with her feet, she is ready to have a new sibling?
And to answer my own question title, YES, there IS SOMETHING inside everyone's body. The heart, the lungs, the kidneys, the ovaries, the gut and all sorts of organs that I can't think of right now.
And I have to agree to disagree that some people (including me) are still living in the past. Has anyone of you watched Romeo (the sitcom)? - that's 1 sample of the living-in-past group.