I like to think of myself as a fairly open-minded person.  But human nature is such that once we make up our mind about something, it is almost impossible for us to change it.  Even with the most innocuous things, once we’ve seen something a certain way, we must make heroic efforts to “un-see” it in order to see something else.  This video is an example of that phenomenon – once you’ve accepted that there is another dancer, it is almost impossible to not see “him”.