So I guess I get how this works in theory, but in practice, doesn't a particle going from A-B have SOME kind of effect that is different than if it went from B-C, even without the sensitive thingy? I don't know if it would be from bouncing off other particles on the way, or having some kind of minute gravitational effect on the rest of the universe, or what. And if that is the case, shouldn't the experiments always behave the as if there WERE that sensitive thingy there? Or is it really possible to set it up so there is literally NO difference in all the particle positions in the universe no matter which path is taken?