Exactly.

Sammy the Bull, in an interview a few years ago (NY Times Magazine), said this scene - in which Michael appears to just blank out everything - is exactly what happened when he, a real mob guy, was about to kill someone. He said the filmmakers must have known reallife mobsters to know this.

I think that's one of the greatest scenes in history. And according to Al Pacino, its the scene that kept him on the job.