I went through most of the film thinking that the dead boy was Saul's son, but at the end of the film I decided he was not. Thoughts?
Also, is the boy at the end of the film that Saul sees in the doorway a vision, or is he really there?
The boy he sees at the end is clearly a vision seeing as how nobody else reacted to him. As for him being his son, it's left open for interpretation.
He very well could be his son as there is a subtle hint that he had the kid with Ella, and it's also completely possible that he is lying/mistaken and is saving the boy's body purly as a means of retaining whatever little humanity is left within him, if any. It works both ways.
The practice of gluing the performances of two different actors together needs to come to an end.