Take a look at this 17-second video.
In the video below, the maker of that video explains what is going on, especially at the 1:35 mark. (You can go to ‘Settings’ and turn on the auto-translate mode if you do not speak Portugese.)
Unless there really are ghosts.
[For some reason, Kaufman’s post has disappeared but the comments to it are still there. But Owlmirror at comment #5 has found a cached page.-MS]