After being told to ‘take a good look’ at his brother, Dean did not even once glance at Sam for the rest of this scene. I thought it was really interesting when I was going through my re-watch. Dean Winchester has always been a determined person and turning to look at his brother meant that he would be losing and admitting defeat. And Dean was going to get his brother out of there. Dean was going to make sure he and Sam got out together. Dean was going to get them out of there safely. So Dean Winchester wasn’t going to take a good look at Sam because he was going to see him again.