Carlson's last Line

I thought that when Steinbeck ended the book with Carson saying " Now what the hell ya suppose is eatin' them two guys?" that he was talking about what caused George and Lennie to care about each other in a genuine friend and what caused George to kill Lennie if they were such good friends. I understand why George killed Lennie but I also understand were Carlson is coming from. I would never kill a good friend even if they have done something bad like what Lennie did.

What do you guys think about what Carlson said?