The first time I smoked weed we were driving by a graveyard and out of the corner of my eye I saw a white figure running along the footpath and then asked in these words to a friend sitting on the same side of the car as me in these words "Did you see that?" and he was able to explain in a very surprised tone that he had seen what I had.
I have no real beliefs regarding this as there is no way of proving or disproving this theory and although science and todays knowledge disagrees with the whole idea of spirits I believe that there are still things that are undiscovered throughout our planet (and universe for that matter).