Update:  US is that rare horror film that improves with a second viewing.  I was impressed with it the first time, but my viewing intent was different the second time.  Knowing the story, I wanted to see if the “gaps” I found during my first viewing were actually there, or were a result of my missing something.
   
I’d missed something.
   
There are quite a few cross references in the film, not only to other moments or characters in the film, but also to other stories and films.  They were so obvious this second time through.  It is brilliantly constructed.
   
I can’t wait to show US to someone who hasn’t seen it before and have a fascinating discussion afterward.