The invisible man
There was a horror movie about an invisible man who becomes invisible after an experiment was performed on him. But shortly after the successful experiment was completed, he begins to lose his mind and go on a killing spree. We are not sure if that would happen here, it seems way less sinister and menacing than in the film.
Here we do not see anyone because there is just nobody there. It is a clever way to get money while not being present. Someone thought they would be able to collect some poor change from the innovative new act they created using sandals and a box. Although we have to give them credit for their creativity.