But the placebo effect is known about through repeated observation. We know of ways to increase and decrease the placebo, and even the nocebo, which most people don't know about. I would classify these as natural phenomena.No matter where you look to find the definition of supernatural, the placebo effect definitely fits the definition. It is outside scientific understanding or the "laws of nature". Or should I say outside the current scientific understanding or the "laws of nature". Once the "laws of nature" were that man cannot fly, but technology changed that law. We are using the LHC to see if there are other dimensions. What if there are and it is possible to cross over to them? Could this not explain things like ghosts or UFOs, or even totally unexplained disappearances? Like flying once was, don't you think that scientific understanding and the "laws of nature" can change to encompass what is now the supernatural? Quackery aside, science must keep an open mind and constantly challenge the status quo, there is no place in modern science for another Galen!
There is no strong evidence for ghosts and UFOs can be literally anything. There are no examples that cannot be explained through natural means, though.
I do think things that are currently considered supernatural could be determined to be natural through scientific inquiry. Science is open-minded by definition, despite what it's detractors suggest. Evidence is what changes that open mind.